Document use of CC and CFLAGS in more detail (bug 20980, bug 21234).

There are some bug reports from people setting CFLAGS not including a
-O option and then being confused when the build fails.  This patch
addresses this by documenting the proper use of CC and CFLAGS in more
detail - saying what options should go where and specifying the
requirement to compile with optimization.

The previous text incorrectly used @var markup with CC and CFLAGS.
The correct markup for environment variables is @env, but it's also
the case that passing such variables explicitly on the configure
command line is preferred to passing them in the environment, so this
patch changes the documentation to describe passing them on the
command line (and uses @code).

In many cases putting options in the wrong place may in fact work, but
I believe what I've specified is the correct rule for which options to
put where.

	[BZ #20980]
	[BZ #21234]
	* manual/install.texi (Configuring and compiling): Describe
	passing CC and CFLAGS on configure command line, not as
	environment variables.  Use @code markup on those variables.
	Specify what options go in CC and what go in CFLAGS.  Note the
	requirement to compile with optimization.
	* INSTALL: Regenerated.

ChangeLog

@@ -1,5 +1,14 @@
 2018-02-15  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #20980]
+	[BZ #21234]
+	* manual/install.texi (Configuring and compiling): Describe
+	passing CC and CFLAGS on configure command line, not as
+	environment variables.  Use @code markup on those variables.
+	Specify what options go in CC and what go in CFLAGS.  Note the
+	requirement to compile with optimization.
+	* INSTALL: Regenerated.
+
 	[BZ #18124]
 	* sysdeps/hppa/bsd-setjmp.S: Include <sysdep.h>.
 	(setjmp): Use HIDDEN_JUMPTARGET with __sigsetjmp.

INSTALL

@@ -36,9 +36,18 @@ normal setting to install as the standard system library is
 '--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix)
 for GNU/Hurd systems.
 
-   It may also be useful to set the CC and CFLAGS variables in the
+   It may also be useful to pass 'CC=COMPILER' and 'CFLAGS=FLAGS'
-environment when running 'configure'.  CC selects the C compiler that
+arguments to 'configure'.  'CC' selects the C compiler that will be
-will be used, and CFLAGS sets optimization options for the compiler.
+used, and 'CFLAGS' sets optimization options for the compiler.  Any
+compiler options required for all compilations, such as options
+selecting an ABI or a processor for which to generate code, should be
+included in 'CC'.  Options that may be overridden by the GNU C Library
+build system for particular files, such as for optimization and
+debugging, should go in 'CFLAGS'.  The default value of 'CFLAGS' is '-g
+-O2', and the GNU C Library cannot be compiled without optimization, so
+if 'CFLAGS' is specified it must enable optimization.  For example:
+
+     $ ../glibc-VERSION/configure CC="gcc -m32" CFLAGS="-O3"
 
    The following list describes all of the available options for
 'configure':
@@ -210,7 +219,7 @@ will be used, and CFLAGS sets optimization options for the compiler.
      but you want to compile a library for 586es, give
      '--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the
      appropriate compiler flags ('-mcpu=i586' will do the trick) to
-     CFLAGS.
+     'CC'.
 
      If you specify just '--build', 'configure' will get confused.
 
@@ -304,7 +313,7 @@ makefiles.
 setting a few variables in 'configparms'.  Set 'CC' to the
 cross-compiler for the target you configured the library for; it is
 important to use this same 'CC' value when running 'configure', like
-this: 'CC=TARGET-gcc configure TARGET'.  Set 'BUILD_CC' to the compiler
+this: 'configure TARGET CC=TARGET-gcc'.  Set 'BUILD_CC' to the compiler
 to use for programs run on the build system as part of compiling the
 library.  You may need to set 'AR' to cross-compiling versions of 'ar'
 if the native tools are not configured to work with object files for the

manual/install.texi

@@ -59,10 +59,21 @@ but the normal setting to install as the standard system library is
 @samp{--prefix=/usr} for @gnulinuxsystems{} and @samp{--prefix=} (an
 empty prefix) for @gnuhurdsystems{}.
 
-It may also be useful to set the @var{CC} and @var{CFLAGS} variables in
+It may also be useful to pass @samp{CC=@var{compiler}} and
-the environment when running @code{configure}.  @var{CC} selects the C
+@code{CFLAGS=@var{flags}} arguments to @code{configure}.  @code{CC}
-compiler that will be used, and @var{CFLAGS} sets optimization options
+selects the C compiler that will be used, and @code{CFLAGS} sets
-for the compiler.
+optimization options for the compiler.  Any compiler options required
+for all compilations, such as options selecting an ABI or a processor
+for which to generate code, should be included in @code{CC}.  Options
+that may be overridden by the @glibcadj{} build system for particular
+files, such as for optimization and debugging, should go in
+@code{CFLAGS}.  The default value of @code{CFLAGS} is @samp{-g -O2},
+and @theglibc{} cannot be compiled without optimization, so if
+@code{CFLAGS} is specified it must enable optimization.  For example:
+
+@smallexample
+$ ../glibc-@var{version}/configure CC="gcc -m32" CFLAGS="-O3"
+@end smallexample
 
 The following list describes all of the available options for
  @code{configure}:
@@ -241,7 +252,7 @@ if @code{configure} guesses your machine as @code{i686-pc-linux-gnu} but
 you want to compile a library for 586es, give
 @samp{--host=i586-pc-linux-gnu} or just @samp{--host=i586-linux} and add
 the appropriate compiler flags (@samp{-mcpu=i586} will do the trick) to
-@var{CFLAGS}.
+@code{CC}.
 
 If you specify just @samp{--build}, @code{configure} will get confused.
 
@@ -339,8 +350,8 @@ It is easy to configure @theglibc{} for cross-compilation by
 setting a few variables in @file{configparms}.  Set @code{CC} to the
 cross-compiler for the target you configured the library for; it is
 important to use this same @code{CC} value when running
-@code{configure}, like this: @samp{CC=@var{target}-gcc configure
+@code{configure}, like this: @samp{configure @var{target}
-@var{target}}.  Set @code{BUILD_CC} to the compiler to use for programs
+CC=@var{target}-gcc}.  Set @code{BUILD_CC} to the compiler to use for programs
 run on the build system as part of compiling the library.  You may need to
 set @code{AR} to cross-compiling versions of @code{ar}
 if the native tools are not configured to work with