Revert 0776198486 for Solaris debug

For some reason 0776198486 didn't fail
https://rubyci.org/logs/rubyci.s3.amazonaws.com/solaris10-gcc/ruby-master/log/20200503T230004Z.log.html.gz
even while it was before 9aa5fe1bf8.

Anyway, there's no need to keep the change anymore.

mjit_worker.c

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