gnulib: install the environ module

This should fix compilation on OSX, as reported by Yann Thierry-Mieg.

* m4/environ.m4: New file.
* m4/gnulib-cache.m4, m4/gnulib-comp.m4: Update.
* bin/common_trans.cc [HAVE_SPAWN_H]: Do not define environ.

m4/environ.m4

@@ -0,0 +1,46 @@
+# environ.m4 serial 8
+dnl Copyright (C) 2001-2004, 2006-2021 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN_ONCE([gl_ENVIRON],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  dnl Persuade glibc <unistd.h> to declare environ.
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  AC_CHECK_HEADERS_ONCE([unistd.h])
+  gt_CHECK_VAR_DECL(
+    [#if HAVE_UNISTD_H
+     #include <unistd.h>
+     #endif
+     /* mingw, BeOS, Haiku declare environ in <stdlib.h>, not in <unistd.h>.  */
+     #include <stdlib.h>
+    ],
+    [environ])
+  if test $gt_cv_var_environ_declaration != yes; then
+    HAVE_DECL_ENVIRON=0
+  fi
+])
+
+# Check if a variable is properly declared.
+# gt_CHECK_VAR_DECL(includes,variable)
+AC_DEFUN([gt_CHECK_VAR_DECL],
+[
+  define([gt_cv_var], [gt_cv_var_]$2[_declaration])
+  AC_CACHE_CHECK([if $2 is properly declared], [gt_cv_var],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[$1
+            typedef struct { int foo; } foo_t;
+            extern foo_t $2;]],
+          [[$2.foo = 1;]])],
+       [gt_cv_var=no],
+       [gt_cv_var=yes])])
+  if test $gt_cv_var = yes; then
+    AC_DEFINE([HAVE_]m4_translit($2, [a-z], [A-Z])[_DECL], 1,
+              [Define if you have the declaration of $2.])
+  fi
+  undefine([gt_cv_var])
+])