dockcross: Add support for Windows

Tested on Git Bash and Bash on Ubuntu for Windows.

There are some issue with building the Docker image itself, but using the
images works great.

Makefile

@@ -10,7 +10,7 @@ DOCKER = docker
 ORG = dockcross
 
 # Directory where to generate the dockcross script for each images (e.g bin/dockcross-manylinux-x64)
-BIN = bin
+BIN = ./bin
 
 # These images are built using the "build implicit rule"
 STANDARD_IMAGES = android-arm linux-x86 linux-x64 linux-arm64 linux-armv5 linux-armv6 linux-armv7 linux-ppc64le windows-x86 windows-x64
@@ -95,7 +95,7 @@ manylinux-x86.test: manylinux-x86
 Dockerfile: Dockerfile.in common.docker
 	sed '/common.docker/ r common.docker' Dockerfile.in > Dockerfile
 
-base: Dockerfile
+base: Dockerfile imagefiles/
 	$(DOCKER) build -t $(ORG)/base \
 		--build-arg IMAGE=$(ORG)/base \
 		--build-arg VCS_REF=`git rev-parse --short HEAD` \

imagefiles/dockcross

@@ -171,18 +171,35 @@ fi
 # Set the docker run extra args (if any)
 FINAL_ARGS=${ARG_ARGS-${DOCKCROSS_ARGS}}
 
-# If we are not running via boot2docker
-if [ -z $DOCKER_HOST ]; then
+# Bash on Ubuntu on Windows
+UBUNTU_ON_WINDOWS=$(grep -l Microsoft /proc/version)
+# MSYS, Git Bash, etc.
+MSYS=$(grep -l MINGW /proc/version)
+
+if [ -z "$UBUNTU_ON_WINDOWS" -a -z "$MSYS" ]; then
     USER_IDS="-e BUILDER_UID=$( id -u ) -e BUILDER_GID=$( id -g ) -e BUILDER_USER=$( id -un ) -e BUILDER_GROUP=$( id -gn )"
 fi
 
+# Change the PWD when working in Docker on Windows
+if [ -n "$UBUNTU_ON_WINDOWS" ]; then
+    HOST_PWD=$PWD
+    HOST_PWD=${HOST_PWD/\/mnt\//}
+    HOST_PWD=${HOST_PWD/\//:\/}
+elif [ -n "$MSYS" ]; then
+    HOST_PWD=$PWD
+    HOST_PWD=${HOST_PWD/\//}
+    HOST_PWD=${HOST_PWD/\//:\/}
+else
+    HOST_PWD=$PWD
+fi
+
 #------------------------------------------------------------------------------
 # Now, finally, run the command in a container
 #
 tty -s && TTY_ARGS=-ti || TTY_ARGS=
 CONTAINER_NAME=dockcross_$RANDOM
 docker run $TTY_ARGS --name $CONTAINER_NAME \
-    -v $PWD:/work \
+    -v $HOST_PWD:/work \
     $USER_IDS \
     $FINAL_ARGS \
     $FINAL_IMAGE "$@"