Build a mingw32-make.exe when cross building toolchains

This can be used e.g. for building Qt without any MSYS installation,
and should also work for cmake, if using the mingw makefiles
generator.

Dockerfile.cross

@@ -40,6 +40,9 @@ RUN ./install-wrappers.sh $CROSS_TOOLCHAIN_PREFIX --host=$HOST
 COPY prepare-cross-toolchain.sh .
 RUN ./prepare-cross-toolchain.sh $TOOLCHAIN_PREFIX $CROSS_TOOLCHAIN_PREFIX $CROSS_ARCH
 
+COPY build-make.sh .
+RUN ./build-make.sh $CROSS_TOOLCHAIN_PREFIX --host=$HOST
+
 ARG TAG
 RUN ln -s $CROSS_TOOLCHAIN_PREFIX llvm-mingw && \
     zip -9r /llvm-mingw-$TAG$CROSS_ARCH.zip llvm-mingw && \

build-cross-tools.sh

@@ -18,3 +18,4 @@ HOST=$CROSS_ARCH-w64-mingw32
 ./build-mingw-w64.sh $PREFIX --skip-include-triplet-prefix --host=$HOST
 ./install-wrappers.sh $PREFIX --host=$HOST
 ./prepare-cross-toolchain.sh $NATIVE $PREFIX $CROSS_ARCH
+./build-make.sh $PREFIX --host=$HOST

build-make.sh

@@ -0,0 +1,57 @@
+#!/bin/sh
+
+set -e
+
+unset HOST
+
+: ${MAKE_VERSION:=4.2.1}
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+    --host=*)
+        HOST="${1#*=}"
+        ;;
+    *)
+        PREFIX="$1"
+        ;;
+    esac
+    shift
+done
+if [ -z "$PREFIX" ]; then
+    echo $0 [--host=<triple>] dest
+    exit 1
+fi
+
+mkdir -p "$PREFIX"
+PREFIX="$(cd "$PREFIX" && pwd)"
+
+: ${CORES:=$(nproc 2>/dev/null)}
+: ${CORES:=$(sysctl -n hw.ncpu 2>/dev/null)}
+: ${CORES:=4}
+: ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
+
+download() {
+    if [ -n "$(which wget)" ]; then
+        wget "$1"
+    else
+        curl -LO "$1"
+    fi
+}
+
+if [ ! -d make-$MAKE_VERSION ]; then
+    download https://ftp.gnu.org/gnu/make/make-$MAKE_VERSION.tar.bz2
+    tar -jxf make-$MAKE_VERSION.tar.bz2
+fi
+
+cd make-$MAKE_VERSION
+
+if [ -n "$HOST" ]; then
+    CONFIGFLAGS="$CONFIGFLAGS --host=$HOST"
+    CROSS_NAME=-$HOST
+fi
+
+mkdir -p build$CROSS_NAME
+cd build$CROSS_NAME
+../configure --prefix="$PREFIX" $CONFIGFLAGS --program-prefix=mingw32- --enable-job-server LDFLAGS="-Wl,-s"
+make -j$CORES
+make install-binPROGRAMS