[PATCH] configure: disable split_debug on Windows and on non-git builds

[Paolo Bonzini <pbonzini@redhat.com>]

-gsplit-dwarf is reported to produce broken binaries on Windows.
The linker produces warnings but exits successfully:

/usr/lib/gcc/x86_64-w64-mingw32/14.2.0/../../../../x86_64-w64-mingw32/bin/ld:
qga/qemu-ga.exe:/4: section below image base
/usr/lib/gcc/x86_64-w64-mingw32/14.2.0/../../../../x86_64-w64-mingw32/bin/ld:
qga/qemu-ga.exe:/24: section below image base

and as a result qemu-ga.exe fails to start.

On top of this, also disable -gsplit-dwarf unless building from git.
Similar to -Werror, split debug info is probably not the best choice
for people that want to build for installing.

(Random thoughts: there is a tension here between adding an option
that is useful for QEMU developers, and messing things up for everyone
else by doing something decidedly non-standard.  For example, distros
are starting to create a fake git repository just so that they can
use "git am" to apply patches; while some of them, for example Fedora,
are wise, or paranoid, enough to pass --disable-XXX for everything and
then turn back on what they want, it cannot be expected that everyone
does this.  It may be safer to make --enable-split-debug default off
for everybody and add it somewhere in docs/.  For now I am keeping it
enabled but we could consider doing something different during the hard
freeze period).

Reported-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 configure         | 4 ++++
 meson_options.txt | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 02f1dd2311f..9aece67ed08 100755
--- a/configure
+++ b/configure
@@ -1864,6 +1864,10 @@ if test "$skip_meson" = no; then
       { test "$host_os" = linux || test "$host_os" = "windows"; }; then
       echo 'werror = true' >> $cross
   fi
+  if test -e "$source_path/.git" && test "$host_os" != "windows"; then
+      echo 'split_debug = true' >> $cross
+  fi
+
   echo "[project options]" >> $cross
   if test "$SMBD" != ''; then
     echo "smbd = $(meson_quote "$SMBD")" >> $cross
diff --git a/meson_options.txt b/meson_options.txt
index 3432123fee2..f3546b9abc1 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -362,7 +362,7 @@ option('debug_mutex', type: 'boolean', value: false,
        description: 'mutex debugging support')
 option('debug_stack_usage', type: 'boolean', value: false,
        description: 'measure coroutine stack usage')
-option('split_debug', type: 'boolean', value: true,
+option('split_debug', type: 'boolean', value: false,
        description: 'split debug info from object files')
 option('qom_cast_debug', type: 'boolean', value: true,
        description: 'cast debugging support')
-- 
2.48.1