Add libgmp

recipes/gnu-binutils/recipe.sh

 GIT=https://gitlab.redox-os.org/redox-os/binutils-gdb.git
 BRANCH=redox
 GIT_UPSTREAM=git://sourceware.org/git/binutils-gdb.git
-BUILD_DEPENDS=(expat)
+BUILD_DEPENDS=(expat libgmp)
 
 function recipe_version {
     printf "r%s.%s" "$(git rev-list --count HEAD)" "$(git rev-parse --short HEAD)"

recipes/libgmp/recipe.toml

+[source]
+tar = "https://gmplib.org/download/gmp/gmp-6.2.1.tar.xz"
+
+[build]
+template = "configure"