gpgme: fix build on darwin

pkgs/development/libraries/gpgme/default.nix

@@ -34,7 +34,9 @@ stdenv.mkDerivation rec {
       sha256 = "00d4sxq63601lzdp2ha1i8fvybh7dzih4531jh8bx07fab3sw65g";
     })
     # Disable python tests on Darwin as they use gpg (see configureFlags below)
-  ] ++ lib.optional stdenv.isDarwin ./disable-python-tests.patch;
+  ] ++ lib.optional stdenv.isDarwin ./disable-python-tests.patch
+  # Fix _AC_UNDECLARED_WARNING for autoconf≥2.70. See https://lists.gnupg.org/pipermail/gnupg-devel/2020-November/034643.html
+  ++ lib.optional stdenv.cc.isClang ./fix-clang-autoconf-undeclared-warning.patch;
 
   outputs = [ "out" "dev" "info" ];
   outputBin = "dev"; # gpgme-config; not so sure about gpgme-tool

pkgs/development/libraries/gpgme/fix-clang-autoconf-undeclared-warning.patch

@@ -0,0 +1,36 @@
+diff -Naur gpgme.old/configure.ac gpgme.new/configure.ac
+--- gpgme.old/configure.ac	2020-11-12 04:19:50.000000000 -0500
++++ gpgme.new/configure.ac	2021-01-08 03:04:38.000000000 -0500
+@@ -166,6 +166,16 @@
+                           mym4_minor mym4_micro)
+ AC_SUBST(VERSION_NUMBER)
+ 
++# Try to find a thread-safe version of ttyname().
++gnupg_REPLACE_TTYNAME_R
++if test "$ac_cv_func_ttyname_r" != yes; then
++  AC_MSG_WARN([
++***
++*** ttyname() is not thread-safe and ttyname_r() does not exist
++***])
++fi
++
++
+ # We need to compile and run a program on the build machine.  A
+ # comment in libgpg-error says that the AC_PROG_CC_FOR_BUILD macro in
+ # the AC archive is broken for autoconf 2.57.  Given that there is no
+@@ -658,15 +668,6 @@
+ 
+ AC_FUNC_FSEEKO
+ 
+-# Try to find a thread-safe version of ttyname().
+-gnupg_REPLACE_TTYNAME_R
+-if test "$ac_cv_func_ttyname_r" != yes; then
+-  AC_MSG_WARN([
+-***
+-*** ttyname() is not thread-safe and ttyname_r() does not exist
+-***])
+-fi
+-
+ # Try to find a thread-safe version of getenv().
+ have_thread_safe_getenv=no
+ jm_GLIBC21