[PATCH] AC_USE_SYSTEM_EXTENSIONS: Set _COSMO_SOURCE

[Jack Kelly]

This enables extensions when compiling with Cosmopolitan Libc.
https://justine.lol/cosmopolitan/

* lib/autoconf/specific.m4: Define _COSMO_SOURCE.
* doc/autoconf.texi: Document that we now set _COSMO_SOURCE.
---
 NEWS                     | 3 +++
 doc/autoconf.texi        | 2 ++
 lib/autoconf/specific.m4 | 5 +++++
 3 files changed, 10 insertions(+)

diff --git a/NEWS b/NEWS
index 9e68534f..42af6d54 100644
--- a/NEWS
+++ b/NEWS
@@ -165,6 +165,9 @@ GNU Autoconf NEWS - User visible changes.
 *** AC_USE_SYSTEM_EXTENSIONS now enables C23 Annex F extensions
   by defining __STDC_WANT_IEC_60559_EXT__.
 
+*** AC_USE_SYSTEM_EXTENSIONS now supports Cosmopolitan Libc
+  by defining _COSMO_SOURCE.
+
 ** Obsolete features and new warnings
 
 *** Autoconf now quotes 'like this' instead of `like this'.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index f202ea00..bbf2a117 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -8914,6 +8914,8 @@ The following preprocessor macros are defined 
unconditionally:
 @item _ALL_SOURCE
 @cvindex _ALL_SOURCE
 Enable extensions on AIX 3 and Interix.
+@item _COSMO_SOURCE
+Enable extensions on Cosmopolitan Libc.
 @item _DARWIN_C_SOURCE
 @cvindex _DARWIN_C_SOURCE
 Enable extensions on macOS.
diff --git a/lib/autoconf/specific.m4 b/lib/autoconf/specific.m4
index b758c7d1..efdf20ac 100644
--- a/lib/autoconf/specific.m4
+++ b/lib/autoconf/specific.m4
@@ -551,6 +551,10 @@ AH_VERBATIM([USE_SYSTEM_EXTENSIONS],
 #ifndef _ALL_SOURCE
 # undef _ALL_SOURCE
 #endif
+/* Enable extensions on Cosmopolitan Libc. */
+#ifndef _COSMO_SOURCE
+# undef _COSMO_SOURCE
+#endif
 /* Enable general extensions on macOS.  */
 #ifndef _DARWIN_C_SOURCE
 # undef _DARWIN_C_SOURCE
@@ -677,6 +681,7 @@ dnl it should only be defined when necessary.
           [ac_cv_should_define__xopen_source=yes])])])])
 
   AC_DEFINE([_ALL_SOURCE])
+  AC_DEFINE([_COSMO_SOURCE])
   AC_DEFINE([_DARWIN_C_SOURCE])
   AC_DEFINE([_GNU_SOURCE])
   AC_DEFINE([_HPUX_ALT_XOPEN_SOCKET_API])
-- 
2.44.1