1.3 fails to build on Ubuntu 19.04

[vcosta]

It claims it cannot find the symbol for 'pthread_create' in the cmake stage.

[franz]

Taking a docker file from tools/docker/Ubuntu and adjusting it to use 19.04 base image:

FROM amd64/ubuntu:19.04

ARG GIT_COMMIT=master
LABEL git-commit=$GIT_COMMIT vendor=pocl distro=Ubuntu version=1.0
ENV TERM dumb

RUN apt update
RUN apt upgrade -y
RUN apt install -y build-essential ocl-icd-libopencl1 cmake git pkg-config libclang-dev clang llvm make ninja-build ocl-icd-libopencl1 ocl-icd-dev ocl-icd-opencl-dev libhwloc-dev zlib1g zlib1g-dev clinfo
RUN cd /home ; git clone https://github.com/pocl/pocl.git ; cd /home/pocl ; git checkout $GIT_COMMIT

RUN cd /home/pocl ; mkdir b ; cd b; cmake -DCMAKE_INSTALL_PREFIX=/usr -G Ninja ..
RUN cd /home/pocl/b ; ninja
CMD cd /home/pocl/b ; clinfo ; ctest -j4 --output-on-failure -L internal

... seems to build & run without any issues.