Make spirv.pc self-contained (#951988)

This closes RC bug #951988 and adds an autopkgtest to make sure it doesn't come back.

• Add missing dependencies to spirv.pc

  Some code accessed via spirv.pc requires SPIRV-Tools and/or glslang.

  Closes: #951988

• d/tests/glslang-dev: Add a test for spirv.pc

  Reproduces: #951988