Ensure FreeType compiles with pthreads support when necessary.

[Asaaj]

This solves an error similar to those discussed in #8503, in which a program which needed both pthreads and freetype was failing to compile with this error:

wasm-ld: error: 'atomics' feature is disallowed by sfnt.c.o, so --shared-memory must not be used

Making this change locally solved the issue. Solved in the same style as #8960.

[sbc100]

Can you modify the test_freetype test in test_other.py. Presumably adding -sUSE_PTHREADS to that test will cause it to fail (without this patch).

[Asaaj]

I verified the new test does fail without these changes

[sbc100]

You don't need the try catch. Just the one self.emcc line is enough (and the comment).

[Asaaj]

Fair enough, I amended in the fork to keep it cleaner

[sbc100]

Actually there is one more detail we forgot to consider here. The other ports that have multi-threaded variants use an alternative name (i.e. the -mt) suffice. See tools/ports/icu.py for an example.

We have two options here I think:

1. Introduce a -mt variant filename when building with pthreads
2. Always build with pthreads assuming that the runtime/browser will accept the atomic access even in single threaded mode (see Allowing atomic instructions with unshared memory WebAssembly/threads#144).

The later option would keep the code simpler. If (2) works and we can pass both the theaded and non-threaded tests then I think it would be preferable. All you would need to do it simply always pass -sUSE_PTHREADS (actually can you pass the standard -pthread flag instead?)

[Asaaj]

In my current configuration, I am unable to run the other tests in general. I get a huge number of exceptions, and it's unable to import acorn. I assume I can follow a guide to solve that, but would this change be something you'd be able to verify the correctness of more easily? If not, I won't be able to get to it until next week

[sbc100]

In my current configuration, I am unable to run the other tests in general. I get a huge number of exceptions, and it's unable to import acorn. I assume I can follow a guide to solve that, but would this change be something you'd be able to verify the correctness of more easily? If not, I won't be able to get to it until next week

Maybe you didn't run npm install?