configure: don't enable ASLR for --enable-debug Windows builds

Unlike other OSs it is not possible for gdb to temporarily disable ASLR when
debugging executables on Windows which causes gdb to fail with memory access
errors when trying to debug QEMU.

Keep ASLR enabled by default on Windows via the --dynamicbase compiler flag
except for --enable-debug builds when there is a clear expectation that a
functioning gdb is expected at the cost of slightly less security.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20201005133434.12614-1-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -5882,7 +5882,14 @@ fi
 
 # Use ASLR, no-SEH and DEP if available
 if test "$mingw32" = "yes" ; then
-    for flag in --dynamicbase --no-seh --nxcompat; do
+    flags="--no-seh --nxcompat"
+
+    # Disable ASLR for debug builds to allow debugging with gdb
+    if test "$debug" = "no" ; then
+        flags="--dynamicbase $flags"
+    fi
+
+    for flag in $flags; do
         if ld_has $flag ; then
             QEMU_LDFLAGS="-Wl,$flag $QEMU_LDFLAGS"
         fi