Do not anger the libgmp Elder Gods

configure.ac

@@ -700,7 +700,7 @@ if test x$use_pkgconfig = xyes; then
   )
 else
   # BUG: Fix this:
-  echo 'BUG: configure does not yet check for the following dependencies if pkg-config is not on the system: libcrypto++'
+  echo 'BUG: configure does not yet check for the following dependencies if pkg-config is not on the system: libcrypto++, gmp'
 
   AC_CHECK_HEADER([openssl/crypto.h],,AC_MSG_ERROR(libcrypto headers missing))
   AC_CHECK_LIB([crypto],      [main],CRYPTO_LIBS=-lcrypto, AC_MSG_ERROR(libcrypto missing))
@@ -716,6 +716,22 @@ else
     fi
   fi
 
+# These packages don't provide pkgconfig config files across all
+# platforms, so we use older autoconf detection mechanisms:
+if test x$TARGET_OS = xdarwin; then
+AC_CHECK_HEADER([gmp.h],,AC_MSG_ERROR(libgmp headers missing))
+AC_CHECK_LIB([gmp],[[__gmpn_sub_n]],GMP_LIBS=-lgmp, [AC_MSG_ERROR(libgmp missing)])
+
+AC_CHECK_HEADER([gmpxx.h],,AC_MSG_ERROR(libgmpxx headers missing))
+AC_CHECK_LIB([gmpxx],[main],GMPXX_LIBS=-lgmpxx, [AC_MSG_ERROR(libgmpxx missing)])
+fi
+
+#AC_CHECK_HEADER([gmp.h],,AC_MSG_ERROR(libgmp headers missing))
+#AC_CHECK_LIB([gmp],[[__gmpn_sub_n]],GMP_LIBS=-lgmp, [AC_MSG_ERROR(libgmp missing)])
+
+#AC_CHECK_HEADER([gmpxx.h],,AC_MSG_ERROR(libgmpxx headers missing))
+#AC_CHECK_LIB([gmpxx],[main],GMPXX_LIBS=-lgmpxx, [AC_MSG_ERROR(libgmpxx missing)])
+
   if test "x$use_zmq" = "xyes"; then
      AC_CHECK_HEADER([zmq.h],
        [AC_DEFINE([ENABLE_ZMQ],[1],[Define to 1 to enable ZMQ functions])],
@@ -754,7 +770,7 @@ AX_CHECK_COMPILE_FLAG([-fwrapv],[CXXFLAGS="$CXXFLAGS -fwrapv"])
 AX_CHECK_COMPILE_FLAG([-fno-strict-aliasing],[CXXFLAGS="$CXXFLAGS -fno-strict-aliasing"])
 AX_CHECK_COMPILE_FLAG([-Wno-builtin-declaration-mismatch],[CXXFLAGS="$CXXFLAGS -Wno-builtin-declaration-mismatch"],,[[$CXXFLAG_WERROR]])
 
-LIBZCASH_LIBS="$BOOST_SYSTEM_LIB -lcrypto -lsodium $RUST_LIBS"
+LIBZCASH_LIBS="-lgmp -lgmpxx $BOOST_SYSTEM_LIB -lcrypto -lsodium $RUST_LIBS"
 
 AC_MSG_CHECKING([whether to build komodod])
 AM_CONDITIONAL([BUILD_BITCOIND], [test x$build_bitcoind = xyes])