Debug Solaris's MJIT failure

using -Winvalid-pch

https://rubyci.org/logs/rubyci.s3.amazonaws.com/solaris10-gcc/ruby-master/log/20200501T170004Z.fail.html.gz

mjit_worker.c

@@ -266,7 +266,11 @@ static char *libruby_pathflag;
 #if defined(__GNUC__) && \
      (!defined(__clang__) || \
       (defined(__clang__) && (defined(__FreeBSD__) || defined(__GLIBC__))))
-# define GCC_PIC_FLAGS "-Wfatal-errors", "-fPIC", "-shared", "-w", "-pipe",
+# ifdef __sun
+#  define GCC_PIC_FLAGS "-Winvalid-pch", "-fPIC", "-shared", "-w", "-pipe",
+# else
+#  define GCC_PIC_FLAGS "-Wfatal-errors", "-fPIC", "-shared", "-w", "-pipe",
+# endif
 # define MJIT_CFLAGS_PIPE 1
 #else
 # define GCC_PIC_FLAGS /* empty */

test/lib/jit_support.rb

@@ -56,7 +56,7 @@ module JITSupport
     return @supported if defined?(@supported)
     @supported = RbConfig::CONFIG["MJIT_SUPPORT"] != 'no' && UNSUPPORTED_COMPILERS.all? do |regexp|
       !regexp.match?(RbConfig::CONFIG['MJIT_CC'])
-    end && !appveyor_pdb_corrupted? && !PENDING_RUBYCI_NICKNAMES.include?(ENV['RUBYCI_NICKNAME']) && /mingw/ !~ RUBY_PLATFORM && /solaris/ !~ RUBY_PLATFORM # TODO: remove mingw / solaris exclusion after investigation
+    end && !appveyor_pdb_corrupted? && !PENDING_RUBYCI_NICKNAMES.include?(ENV['RUBYCI_NICKNAME']) && /mingw/ !~ RUBY_PLATFORM # TODO: remove mingw exclusion after investigation
   end
 
   # AppVeyor's Visual Studio 2013 / 2015 are known to spuriously generate broken pch / pdb, like: