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.
# setup: import numpy as np ; N = 50 ; X, Y = np.random.randn(30,N), np.random.randn(20,N)
# run: allpairs_distances_loops(X, Y)

# pythran export allpairs_distances_loops(float64[][], float64[][])
import numpy as np


def allpairs_distances_loops(X, Y):
    result = np.zeros((X.shape[0], Y.shape[0]), X.dtype)
    for i in range(X.shape[0]):
        for j in range(Y.shape[0]):
            result[i, j] = np.sum((X[i, :] - Y[j, :]) ** 2)
    return result

# setup: import numpy as np ; N = 50 ; X, Y = np.random.randn(30,N), np.random.randn(20,N)
# run: allpairs_distances_loops(X, Y)

# pythran export allpairs_distances_loops(float64[][], float64[][])
import numpy as np


def allpairs_distances_loops(X, Y):
    result = np.zeros((X.shape[0], Y.shape[0]), X.dtype)
    for i in range(X.shape[0]):
        for j in range(Y.shape[0]):
            result[i, j] = np.sum((X[i, :] - Y[j, :]) ** 2)
    return result
