diff --git a/config.sh b/config.sh
index ec3c1ce..844fb3d 100644
--- a/config.sh
+++ b/config.sh
@@ -1,13 +1,15 @@
 # ARCH will be auto-detected as the host if not specified
 #ARCH=i486
-#ARCH=x86_64
+ARCH=x86_64
 #ARCH=powerpc
 #ARCH=arm
 #ARCH=microblaze
 #ARCH=mips
 #ARCH=mipsel
 
-CC_BASE_PREFIX=/opt/cross
+if [ -z "$CC_BASE_PREFIX" ]; then
+	CC_BASE_PREFIX=$HOME/heads/install
+fi
 
 # If you use arm, you may need more fine-tuning:
 # arm hardfloat v7
@@ -20,11 +22,14 @@ CC_BASE_PREFIX=/opt/cross
 #GCC_BOOTSTRAP_CONFFLAGS="--with-arch=armv7-a --with-float=softfp"
 #GCC_CONFFLAGS="--with-arch=armv7-a --with-float=softfp"
 
-MAKEFLAGS=-j8
+MAKEFLAGS=-j`nproc`
 
 # Enable this to build the bootstrap gcc (thrown away) without optimization, to reduce build time
 GCC_STAGE1_NOOPT=1
 
+# Build GMP, MPFR and MPC
+GCC_BUILTIN_PREREQS=yes
+
 # uncomment these to get smaller/stripped binaries
 #export CFLAGS="-Os -g0 -s"
 #export CXXFLAGS="-Os -g0"
--- /dev/null	2019-10-28 16:42:28.211999999 +0100
+++ musl-cross/hashes/gmp-6.1.0.tar.bz2.sha256	2019-10-29 13:08:53.288687684 +0100
@@ -0,0 +1 @@
+498449a994efeba527885c10405993427995d3f86b8768d8cdf8d9dd7c6b73e8  gmp-6.1.0.tar.bz2
--- /dev/null	2019-10-28 16:42:28.211999999 +0100
+++ musl-cross/hashes/mpfr-3.1.4.tar.bz2.sha256	2019-10-29 13:08:53.292687684 +0100
@@ -0,0 +1 @@
+d3103a80cdad2407ed581f3618c4bed04e0c92d1cf771a65ead662cc397f7775  mpfr-3.1.4.tar.bz2
--- /dev/null	2019-10-28 16:42:28.211999999 +0100
+++ musl-cross/hashes/mpc-1.0.3.tar.gz.sha256	2019-10-29 13:08:53.296687684 +0100
@@ -0,0 +1 @@
+617decc6ea09889fb08ede330917a00b16809b8db88c29c31bfbb49cbf88ecc3  mpc-1.0.3.tar.gz