[Build] Check for libgmp directly

Refactors the libgmp check during configure to use pkgconfig if available, and fallback to using autoconf's check header/check lib.

Removes the m4 script as these checks can just be done directly in configure.ac.

Author: Fuzzbawls

build-aux/m4/gmp.m4

@@ -1168,6 +1168,7 @@ if test x$use_pkgconfig = xyes; then
           PKG_CHECK_MODULES([EVENT_PTHREADS], [libevent_pthreads], [], [AC_MSG_ERROR([libevent_pthreads not found.])])
         fi
         PKG_CHECK_MODULES([SODIUM], [libsodium], [], [AC_MSG_ERROR([libsodium not found.])])
+        PKG_CHECK_MODULES([GMP], [gmp], [], [AC_MSG_ERROR([libgmp not found.])])
       fi
 
       if test "x$use_zmq" = "xyes"; then
@@ -1191,6 +1192,8 @@ else
     fi
     AC_CHECK_HEADER([sodium/core.h], [], [AC_MSG_ERROR([libsodium headers missing])])
     AC_CHECK_LIB([sodium], [main], [SODIUM_LIBS=-lsodium], [AC_MSG_ERROR([libsodium missing])])
+    AC_CHECK_HEADER([gmp.h], [], [AC_MSG_ERROR([libgmp headers missing])])
+    AC_CHECK_LIB([gmp], [__gmpz_init], [LIBS="$LIBS -lgmp"], [AC_MSG_ERROR([libgmp missing])])
   fi
 
   if test "x$use_zmq" = "xyes"; then
@@ -1224,12 +1227,6 @@ else
   fi
 fi
 
-dnl gmp check
-GMP_CHECK
-if test x"$has_gmp" != x"yes"; then
-  AC_MSG_ERROR([libgmp not found])
-fi
-
 dnl univalue check
 
 need_bundled_univalue=yes