libmpc: improved to find the correct mpfr library and headers

scientific/libmpc/libmpc.conf

@@ -16,5 +16,10 @@
 if atstage toolchain; then
         var_append extraconfopt ' ' "--with-gmp-include=$( pkgprefix -r includedir gmp )"
         var_append extraconfopt ' ' "--with-gmp-lib=$( pkgprefix -r libdir gmp )"
+
+	# help to find the correct mpfr library and headers
+	var_append extraconfopt ' ' "--with-mpfr-include=$( pkgprefix -r includedir mpfr )"
+	var_append extraconfopt ' ' "--with-mpfr-lib=$( pkgprefix -r libdir mpfr )"
+
         var_append extraconfopt ' ' "--enable-shared=no"
 fi