[Bug testsuite/95840] New: Parallel build fails due to missing "gcc/xgcc"

[enrico.scholz+bugsgcc@sigma-chemnitz.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95840

            Bug ID: 95840
           Summary: Parallel build fails due to missing "gcc/xgcc"
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: testsuite
          Assignee: unassigned at gcc dot gnu.org
          Reporter: enrico.scholz+bugsgcc@sigma-chemnitz.de
  Target Milestone: ---

Created attachment 48775
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48775&action=edit
fixes race in "make -j"

When doing a parallel build of gcc (e.g. for OpenEmbedded and using GNU make
4.2), I get often

| make[1]: ...././gcc/xgcc: Command not found
| make[1]: *** [..../gcc/cp/Make-lang.in:178: s-selftest-c++] Error 127
| make[1]: *** Waiting for unfinished jobs....
| make[1]: Leaving directory '..../gcc'
| make: *** [Makefile:4328: all-gcc] Error 2

Makefile does

| include c/Make-lang.in
|   ...
|   C_SELFTEST_DEPS = cc1$(exeext) $(SELFTEST_DEPS)
|   ...
|   s-selftest-c: $(C_SELFTEST_DEPS)
| 
| SELFTEST_DEPS = $(GCC_PASSES) stmp-int-hdrs $(srcdir)/testsuite/selftests

which means that $(SELFTEST_DEPS) are expanded in the language fragment
files before they are defined in the main make file.

Attached patch (against 9.3.0) fixes this.