[libvirt] [PATCH v5 1/6] config-post.h: define __GNUC_PREREQ if not defined

[Fabian Freyer]

Several gnulib headers rely on features.h being included by ctype.h to provide
__GNUC_PREREQ, but on systems without glibc, this is not provided. In these
cases __GNUC_PREREQ gets redefined to 0, which causes build errors from checks
in src/internal.h.
Therefore, define __GNUC_PREREQ as early as possible. config.h is probably the
first header that is included, before any other headers.
---
 config-post.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/config-post.h b/config-post.h
index f43521b..dd69197 100644
--- a/config-post.h
+++ b/config-post.h
@@ -69,3 +69,21 @@
 # undef WITH_SECDRIVER_APPARMOR
 # undef WITH_CAPNG
 #endif /* LIBVIRT_NSS */
+
+/*
+ * Define __GNUC__ to a sane default if it isn't yet defined.
+ * This is done here so that it's included as early as possible; gnulib relies
+ * on this to be defined in features.h, which should be included from ctype.h.
+ * This doesn't happen on many non-glibc systems.
+ * When __GNUC__ is not defined, gnulib defines it to 0, which breaks things.
+ */
+#ifdef __GNUC__
+# ifndef __GNUC_PREREQ
+#  if defined __GNUC__ && defined __GNUC_MINOR__
+#   define __GNUC_PREREQ(maj, min)                                        \
+   ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
+#  else
+#   define __GNUC_PREREQ(maj, min) 0
+#  endif
+# endif
+#endif
-- 
2.5.5