configure: Test for libiberty.a (mingw32)

MinGW-w64 and some versions of MinGW32 don't provide libiberty.a,
so add this library only if it was found.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

configure

@@ -511,7 +511,13 @@ if test "$mingw32" = "yes" ; then
   QEMU_CFLAGS="-DWIN32_LEAN_AND_MEAN -DWINVER=0x501 $QEMU_CFLAGS"
   # enable C99/POSIX format strings (needs mingw32-runtime 3.15 or later)
   QEMU_CFLAGS="-D__USE_MINGW_ANSI_STDIO=1 $QEMU_CFLAGS"
-  LIBS="-lwinmm -lws2_32 -liberty -liphlpapi $LIBS"
+  LIBS="-lwinmm -lws2_32 -liphlpapi $LIBS"
+cat > $TMPC << EOF
+int main(void) { return 0; }
+EOF
+  if compile_prog "" "-liberty" ; then
+    LIBS="-liberty $LIBS"
+  fi
   prefix="c:/Program Files/Qemu"
   mandir="\${prefix}"
   datadir="\${prefix}"