Split out building widl to a separate shell script

When cross compiling a llvm-mingw toolchain, we need to build widl
for the intended host environment as well.

Dockerfile

@@ -32,7 +32,7 @@ RUN ./install-wrappers.sh $TOOLCHAIN_PREFIX && \
     rm -rf /build
 
 # Build MinGW-w64, compiler-rt and mingw-w64's extra libraries
-COPY build-mingw-w64.sh build-compiler-rt.sh build-mingw-w64-libraries.sh ./
+COPY build-mingw-w64.sh build-mingw-w64-widl.sh build-compiler-rt.sh build-mingw-w64-libraries.sh ./
 RUN ./build-mingw-w64.sh $TOOLCHAIN_PREFIX && \
     ./build-compiler-rt.sh $TOOLCHAIN_PREFIX && \
     ./build-mingw-w64-libraries.sh $TOOLCHAIN_PREFIX && \

Dockerfile.dev

@@ -37,7 +37,7 @@ COPY install-wrappers.sh .
 RUN ./install-wrappers.sh $TOOLCHAIN_PREFIX
 
 # Build MinGW-w64
-COPY build-mingw-w64.sh .
+COPY build-mingw-w64.sh build-mingw-w64-widl.sh ./
 RUN ./build-mingw-w64.sh $TOOLCHAIN_PREFIX
 
 # Build compiler-rt

build-mingw-w64-widl.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+set -e
+
+if [ $# -lt 1 ]; then
+    echo $0 dest
+    exit 1
+fi
+PREFIX="$1"
+# Not adding $PREFIX/bin to $PATH here, since that is expected to be
+# a cross toolchain; the compiler is expected to be in $PATH already here.
+
+: ${CORES:=4}
+: ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
+
+if [ -n "$HOST" ]; then
+    CONFIGFLAGS="--host=$HOST"
+    CROSS_NAME=$HOST-
+fi
+
+cd mingw-w64/mingw-w64-tools/widl
+for arch in $ARCHS; do
+    mkdir -p build-$CROSS_NAME$arch
+    cd build-$CROSS_NAME$arch
+    ../configure --prefix=$PREFIX --target=$arch-w64-mingw32 $CONFIGFLAGS INSTALL="install -s"
+    make -j$CORES
+    make install
+    cd ..
+done

build-mingw-w64.sh

@@ -63,12 +63,5 @@ for arch in $ARCHS; do
 done
 cd ..
 
-cd mingw-w64-tools/widl
-for arch in $ARCHS; do
-    mkdir -p build-$arch
-    cd build-$arch
-    ../configure --prefix=$PREFIX --target=$arch-w64-mingw32 INSTALL="install -s"
-    make -j$CORES
-    make install
 cd ..
-done
+./build-mingw-w64-widl.sh "$PREFIX"