vxworks: Fix GCC selftests for *-wrs-vxworks7-* targets

Currently when building a cross-compiler targeting arm-wrs-vxworks7, the
self-tests fail unless the VSB_DIR environment variable is set.

This prevents attempts at designating the location of runtime header
files, libraries or startfiles, which would fail on unset environment
variables and aren't needed for such tests.

gcc/ChangeLog:

	* config/vxworks.h (VXWORKS_ADDITIONAL_CPP_SPEC): Don't include
	VxWorks header files if -fself-test is used.
	(STARTFILE_PREFIX_SPEC): Avoid using VSB_DIR if -fself-test is used.

gcc/config/vxworks.h

@@ -36,11 +36,16 @@ along with GCC; see the file COPYING3.  If not see
 
 /* Since we provide a default -isystem, expand -isystem on the command
    line early.  */
+
+/* Self-tests may be run in contexts where the VxWorks environment isn't
+   available.  Prevent attempts at designating the location of runtime header
+   files, libraries or startfiles, which would fail on unset environment
+   variables and aren't needed for such tests.  */
 #if TARGET_VXWORKS7
 
 #undef VXWORKS_ADDITIONAL_CPP_SPEC
 #define VXWORKS_ADDITIONAL_CPP_SPEC                     \
- "%{!nostdinc:                                          \
+ "%{!nostdinc:%{!fself-test=*:                          \
     %{isystem*}                                         \
     %{mrtp: -idirafter %:getenv(VSB_DIR /h)             \
             -idirafter %:getenv(VSB_DIR /share/h)       \
@@ -49,19 +54,19 @@ along with GCC; see the file COPYING3.  If not see
       ;:    -idirafter %:getenv(VSB_DIR /h)             \
             -idirafter %:getenv(VSB_DIR /share/h)       \
             -idirafter %:getenv(VSB_DIR /krnl/h/system) \
-            -idirafter %:getenv(VSB_DIR /krnl/h/public)}}"
+            -idirafter %:getenv(VSB_DIR /krnl/h/public)}}}"
 
 #else /* TARGET_VXWORKS7 */
 
 #undef VXWORKS_ADDITIONAL_CPP_SPEC
 #define VXWORKS_ADDITIONAL_CPP_SPEC		\
- "%{!nostdinc:					\
+ "%{!nostdinc:%{!fself-test=*:			\
     %{isystem*}					\
     %{mrtp: -idirafter %:getenv(WIND_USR /h)	\
 	    -idirafter %:getenv(WIND_USR /h/wrn/coreip) \
       ;:    -idirafter %:getenv(WIND_BASE /target/h) \
 	    -idirafter %:getenv(WIND_BASE /target/h/wrn/coreip) \
-}}"
+}}}"
 
 #endif
 
@@ -108,7 +113,8 @@ along with GCC; see the file COPYING3.  If not see
 
 #if TARGET_VXWORKS7
 #undef  STARTFILE_PREFIX_SPEC
-#define STARTFILE_PREFIX_SPEC "%:getenv(VSB_DIR /usr/lib/common)"
+#define STARTFILE_PREFIX_SPEC \
+  "%{!fself-test=*:%:getenv(VSB_DIR /usr/lib/common)}"
 #define TLS_SYM "-u __tls__"
 #else
 #define TLS_SYM ""