gettext: On ppc64le, for older versions, use system cdefs.h (#33411)

Co-authored-by: Bernhard Kaindl <43588962+bernhardkaindl@users.noreply.github.com>

var/spack/repos/builtin/packages/gettext/package.py

@@ -58,6 +58,13 @@ class Gettext(AutotoolsPackage, GNUMirrorPackage):
     patch("nvhpc-export-symbols.patch", when="%nvhpc")
     patch("nvhpc-long-width.patch", when="%nvhpc")
 
+    # Apply this only where we know that the system libc is glibc, be very careful:
+    @when("@:0.21.0 target=ppc64le:")
+    def patch(self):
+        for fn in ("gettext-tools/gnulib-lib/cdefs.h", "gettext-tools/libgrep/cdefs.h"):
+            with open(fn, "w") as f:
+                f.write("#include <sys/cdefs.h>\n")
+
     @classmethod
     def determine_version(cls, exe):
         gettext = Executable(exe)