glslang: Enable tests

[OPNA2608]

KhronosGroup/glslang#4140

KhronosGroup/glslang#3799 says that this fails on non-LE platforms, but the problematic tool in question was moved to SPIRV-tools in KhronosGroup/glslang@3a7f787, so that might no longer be an issue…
Making a note to check this out the next time my ppc64 machine is free, and send a follow-up PR to disable them on !stdenv.hostPlatform.isLittleEndian if they still fail.

Fails on non-LE due to different issues, skipping affected part of the tests.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • powerpc64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[OPNA2608]

Making a note to check this out the next time my ppc64 machine is free

Squeezed this in just now. gtest-based test suite has two failures on big-endian.

1. UB in an error message, leading to different output:
   Glsl/CompileToAstTest.FromFile/array_frag fails on s390x because error-message depends on endianness KhronosGroup/glslang#2797
2. Something that looks like an endian-related issue with some strings, and some things not parsing correctly:
   Glsl/GlslNonSemanticShaderDebugInfoSpirv13Test.FromFile/spv_debuginfo_coopmatKHR_comp fails on ppc64 KhronosGroup/glslang#4145

So will skip that part of the tests on BE.