For reasons that are a bit beyond me, `--host` and `PLATFORM_TRIPLET`
seem to be independent, in particular we've had an empty
`PLATFORM_TRIPLET`. This is unfortunate because `PLATFORM_TRIPLET`
is used to generate the SOABI config variable which in turn is used
to decide whether a .so file is a good match for loading. We'd like
for linux Pythons not to try to import emscripten .so files (it
raises `ImportError: some_file.so: invalid ELF header`). Similarly,
we'd like to avoid attempting to load linux .so files in wasm. These
platform tags are our friends.

Anyways, this PR sets `PLATFORM_TRIPLET` and ensures that .so files
built by pywasmcross are tagged with our SOABI tag.

I moved the .so file renaming from pywasmcross to buildpkg just
before running the post script. That is a better place to put it in
case the package wants to look at the .so file after linking it. It
might be surprised that we moved it.

I also improved the error message if we try to `loadWebAssemblyModule`
something that is actually say a Linux .so file and updated get_dynlibs
to filter out .so files that have an incompatible abi tag.
Set PLATFORM_TRIPLET, include platform in so names, only load compatible so files. For reasons that are a bit beyond me, `--host` and `PLATFORM_TRIPLET`
seem to be independent, in particular we've had an empty
`PLATFORM_TRIPLET`. This is unfortunate because `PLATFORM_TRIPLET`
is used to generate the SOABI config variable which in turn is used
to decide whether a .so file is a good match for loading. We'd like
for linux Pythons not to try to import emscripten .so files (it
raises `ImportError: some_file.so: invalid ELF header`). Similarly,
we'd like to avoid attempting to load linux .so files in wasm. These
platform tags are our friends.

Anyways, this PR sets `PLATFORM_TRIPLET` and ensures that .so files
built by pywasmcross are tagged with our SOABI tag.

I moved the .so file renaming from pywasmcross to buildpkg just
before running the post script. That is a better place to put it in
case the package wants to look at the .so file after linking it. It
might be surprised that we moved it.

I also improved the error message if we try to `loadWebAssemblyModule`
something that is actually say a Linux .so file and updated get_dynlibs
to filter out .so files that have an incompatible abi tag.
package:
  name: cffi
  version: 1.15.0
requirements:
  run:
    - pycparser
source:
  url: https://files.pythonhosted.org/packages/00/9e/92de7e1217ccc3d5f352ba21e52398372525765b2e0c4530e6eb2ba9282a/cffi-1.15.0.tar.gz
  sha256: 920f0d66a896c2d99f0adbb391f990a84091179542c205fa53ce5787aff87954
  patches:
    - patches/libffi-config.patch
build:
  script: |
    pip install -t $HOSTSITEPACKAGES cffi==$PKG_VERSION
test:
  imports:
    - cffi
about:
  home: http://cffi.readthedocs.org
  PyPI: https://pypi.org/project/cffi
  summary: Foreign Function Interface for Python calling C code.
  license: MIT

package:
  name: cffi
  version: 1.15.0
requirements:
  run:
    - pycparser
source:
  url: https://files.pythonhosted.org/packages/00/9e/92de7e1217ccc3d5f352ba21e52398372525765b2e0c4530e6eb2ba9282a/cffi-1.15.0.tar.gz
  sha256: 920f0d66a896c2d99f0adbb391f990a84091179542c205fa53ce5787aff87954
  patches:
    - patches/libffi-config.patch
build:
  script: |
    pip install -t $HOSTSITEPACKAGES cffi==$PKG_VERSION
test:
  imports:
    - cffi
about:
  home: http://cffi.readthedocs.org
  PyPI: https://pypi.org/project/cffi
  summary: Foreign Function Interface for Python calling C code.
  license: MIT
