Fixed cross-compiling of alsa-sys (closes #192)

Dockerfile

@@ -12,6 +12,7 @@ RUN apt-get update \
         git \
         gnupg \
         pandoc \
+        pkg-config \
         python-pip \
         python-setuptools \
         python-wheel \
@@ -28,7 +29,7 @@ WORKDIR /toolchain
 # Check out Raspbian cross-compiler (this will work on *ALL* Raspberry Pi versions)
 RUN git clone --depth 1 git://github.com/raspberrypi/tools.git rpi-tools \
     && rm -rf rpi-tools/.git
-ENV PATH="/toolchain/rpi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/:${PATH}"
+ENV PATH "/toolchain/rpi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/:${PATH}"
 
 # Create wrapper around gcc to point to rpi sysroot
 # Thanks @ https://github.com/herrernst/librespot/blob/build-rpi/.travis.yml
@@ -38,6 +39,8 @@ RUN echo '#!/bin/sh\narm-linux-gnueabihf-gcc --sysroot /toolchain/rpi-tools/arm-
     && ln -s ld-linux.so.3 rpi-tools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/arm-bcm2708hardfp-linux-gnueabi/sysroot/lib/ld-linux-armhf.so.3
 
 # Install 1.0.x alsa-utils which is needed for compilation
+ENV PKG_CONFIG_ALLOW_CROSS 1
+ENV PKG_CONFIG_PATH "/toolchain/rpi-tools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/arm-bcm2708hardfp-linux-gnueabi/sysroot/lib/pkgconfig"
 RUN curl -O https://www.mirrorservice.org/sites/ftp.alsa-project.org/pub/lib/alsa-lib-1.0.29.tar.bz2 \
     && tar xvjf alsa-lib-1.0.29.tar.bz2 && cd alsa-lib-1.0.29 \
     && CC=arm-linux-gnueabihf-gcc ./configure --host=arm-linux-gnueabihf --disable-python \

build.sh

@@ -17,7 +17,7 @@ export CARGO_TARGET_DIR="/build"
 export CARGO_HOME="/build/cache"
 
 # Install the gcc wrapper in container into cargo
-mkdir /.cargo
+mkdir -p /.cargo
 echo '[target.arm-unknown-linux-gnueabihf]\nlinker = "gcc-wrapper"' > /.cargo/config
 rustup target add arm-unknown-linux-gnueabihf