CI: Add test matrix of gcc versions and QEMU architectures

[t-mat]

#622 (comment)

should we test PPC64LE + gcc v4.8.5 in CI ? and is that even possible btw ?

• It seems we can easily install gcc-[5,11] cross compiler via apt-get.
• I don't know much about gcc-4.8 cross compiler so far.
• We should watch total time of tests.

[t-mat]

I'm working on this issue in my branch
https://github.com/t-mat/xxHash/tree/gha/qemu-gcc-versions

gcc cross compiler versions

• ubuntu-20.04 supports gcc-{8,9,10} cross compiler.
• ubuntu-18.04 supports gcc-{6,7,8} cross compiler.
• I don't know how we can find package of gcc-4.8 and gcc-5 cross compiler for ubunutu-18.04 or 20.04.
• For some reason, ubnutu-20.04 fails to retrieve gcc-8-mips-linux-gnu. As a workaround, I use ubuntu-18.04 for it.
  • We can install all other gcc-8 cross compilers on ubuntu-20.04 though.

Speed

Since all QEMU tests are running in parallel, total duration of CI script isn't changed much.

Ability

Our CI will be able to catch the following error of the issue #622 and PR #631.

xxhash.h: In function ‘XXH3_accumulate_512_vsx’:
xxhash.h:4148:9: error: invalid parameter combination for AltiVec intrinsic
         xxh_u64x2 acc_vec        = vec_xl(0, xacc + 2 * i);
         ^~~~~~~~~
xxhash.h:4158:9: error: invalid parameter combination for AltiVec intrinsic
         vec_xst(acc_vec, 0, xacc + 2 * i);
         ^~~~~~~
<builtin>: recipe for target 'xxhash.o' failed
make: *** [xxhash.o] Error 1

Here's actual build log of "QEMU PPC64, gcc-6".

[Cyan4973]

Excellent @t-mat !