rs6000: Adjust -mdejagnu-cpu to filter out -mtune [PR106345]

As PR106345 shows, when configuring compiler with an explicit
option --with-tune=<value>, it would cause some test cases to
fail if their test points are sensitive to tune setting, such
as: group_ending_nop, loop align etc.  It doesn't help that
even to specify one explicit -mcpu=.

This patch is to adjust the behavior of -mdejagnu-cpu by
filtering out all -mcpu= and -mtune= options, then test cases
would use <cpu> as tune as the one specified by -mdejagnu-cpu.

2022-07-25  Peter Bergner  <bergner@linux.ibm.com>
	    Kewen Lin  <linkw@linux.ibm.com>

	PR testsuite/106345

gcc/ChangeLog:

	* config/rs6000/rs6000.h (DRIVER_SELF_SPECS): Adjust -mdejagnu-cpu
	to filter out all -mtune options.

(cherry picked from commit 75d20d6c84)

gcc/config/rs6000/rs6000.h

@@ -81,12 +81,15 @@
 # define SUBTARGET_DRIVER_SELF_SPECS ""
 #endif
 
-/* Only for use in the testsuite: -mdejagnu-cpu= simply overrides -mcpu=.
+/* Only for use in the testsuite: -mdejagnu-cpu=<value> filters out all
+   -mcpu= as well as -mtune= options then simply adds -mcpu=<value>,
+   while -mdejagnu-tune=<value> filters out all -mtune= options then
+   simply adds -mtune=<value>.
    With older versions of Dejagnu the command line arguments you set in
-   RUNTESTFLAGS override those set in the testcases; with this option,
-   the testcase will always win.  Ditto for -mdejagnu-tune=.  */
+   RUNTESTFLAGS override those set in the testcases; with these options,
+   the testcase will always win.  */
 #define DRIVER_SELF_SPECS \
-  "%{mdejagnu-cpu=*: %<mcpu=* -mcpu=%*}", \
+  "%{mdejagnu-cpu=*: %<mcpu=* %<mtune=* -mcpu=%*}", \
   "%{mdejagnu-tune=*: %<mtune=* -mtune=%*}", \
   "%{mdejagnu-*: %<mdejagnu-*}", \
    SUBTARGET_DRIVER_SELF_SPECS