protobuf/m4/ac_system_extensions.m4

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dnl Provide AC_USE_SYSTEM_EXTENSIONS for old autoconf machines.
AC_DEFUN([ACX_USE_SYSTEM_EXTENSIONS],[
ifdef([AC_USE_SYSTEM_EXTENSIONS],[
AC_USE_SYSTEM_EXTENSIONS
],[
AC_BEFORE([$0], [AC_COMPILE_IFELSE])
AC_BEFORE([$0], [AC_RUN_IFELSE])
AC_REQUIRE([AC_GNU_SOURCE])
AC_REQUIRE([AC_AIX])
AC_REQUIRE([AC_MINIX])
AH_VERBATIM([__EXTENSIONS__],
[/* Enable extensions on Solaris. */
#ifndef __EXTENSIONS__
# undef __EXTENSIONS__
#endif
#ifndef _POSIX_PTHREAD_SEMANTICS
# undef _POSIX_PTHREAD_SEMANTICS
#endif
#ifndef _TANDEM_SOURCE
# undef _TANDEM_SOURCE
#endif])
AC_CACHE_CHECK([whether it is safe to define __EXTENSIONS__],
[ac_cv_safe_to_define___extensions__],
[AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([
# define __EXTENSIONS__ 1
AC_INCLUDES_DEFAULT])],
[ac_cv_safe_to_define___extensions__=yes],
[ac_cv_safe_to_define___extensions__=no])])
test $ac_cv_safe_to_define___extensions__ = yes &&
AC_DEFINE([__EXTENSIONS__])
AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
AC_DEFINE([_TANDEM_SOURCE])
])
])