toolchains: Check for GNU make 4.x

GNU make 4.x is needed to cross-compile glibc 2.28 and newer.
This ensures the problem is caught earlier on CentOS release 7.6, whose
default make version remains 3.82.

scripts/build-toolchains.sh

@@ -99,6 +99,13 @@ if [ "${EC2FASTINSTALL}" = true ] ; then
     git submodule deinit "${module}" || :
 
 else
+    "${MAKE}" --version | (
+        read -r makever
+        case ${makever} in
+        'GNU Make '[4-9]\.*|'GNU Make '[1-9][0-9]) ;;
+        *) false ;;
+        esac; ) || die 'obsolete make version; need GNU make 4.x or later'
+
     module_prepare riscv-gnu-toolchain qemu
     module_build riscv-gnu-toolchain --prefix="${RISCV}"
     echo '==>  Building GNU/Linux toolchain'

scripts/build-util.sh

@@ -14,7 +14,7 @@ case ${ncpu} in
 *) export MAKEFLAGS="-j ${ncpu} ${MAKEFLAGS}" ;;
 esac
 
-MAKE=$(command -v gmake || command -v make)
+MAKE=$(command -v gnumake || command -v gmake || command -v make)
 readonly MAKE