update default versions of gcc-dependency math libraries

Makefile

@@ -5,9 +5,9 @@ CONFIG_SUB_REV = 3d5db9ebe860
 BINUTILS_VER = 2.32
 GCC_VER = 8.3.0
 MUSL_VER = 1.1.22
-GMP_VER = 6.1.1
-MPC_VER = 1.0.3
-MPFR_VER = 3.1.4
+GMP_VER = 6.1.2
+MPC_VER = 1.1.0
+MPFR_VER = 4.0.2
 LINUX_VER = 4.4.10
 
 GNU_SITE = https://ftp.gnu.org/pub/gnu