driver: fix environ corruption after putenv() [PR106624]

The bug appeared afte r13-2010-g1270ccda70ca09 "Factor out
jobserver_active_p" slightly changed `putenv()` use from allocating
to non-allocating:

    -xputenv (concat ("MAKEFLAGS=", dup, NULL));
    +xputenv (jinfo.skipped_makeflags.c_str ());

`xputenv()` (and `putenv()`) don't copy strings and only store the
pointer in the `environ` global table. As a result `environ` got
corrupted as soon as `jinfo.skipped_makeflags` store got deallocated.

This started causing bootstrap crashes in `execv()` calls:

    xgcc: fatal error: cannot execute '/build/build/./prev-gcc/collect2': execv: Bad address

The change restores memory allocation for `xputenv()` argument.

gcc/

	PR driver/106624
	* gcc.cc (driver::detect_jobserver): Allocate storage xputenv()
	argument using xstrdup().

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index cac11c1..75ca0ec 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -9182,7 +9182,7 @@ driver::detect_jobserver () const
 {
   jobserver_info jinfo;
   if (!jinfo.is_active && !jinfo.skipped_makeflags.empty ())
-    xputenv (jinfo.skipped_makeflags.c_str ());
+    xputenv (xstrdup (jinfo.skipped_makeflags.c_str ()));
 }
 
 /* Determine what the exit code of the driver should be.  */