zig build system: add LibExeObjStep.installLibraryHeaders

This function is needed when a library exposes one of its own library
dependency's headers as part of its own public API.

Also, improve error message when a file system error occurs during
install file step.
d703270545Andrew Kelley committed on 1/25/2023, 7:45:57 AMparent3ff1f34
5 files changedLine totals unavailable