llvm-diff shows this PR has no changes to amdgcn--amdhsa.bc.
Motivation is that in our downstream the same category of target
built-ins, e.g. math, are organized in several different folders. For
example, in target SOURCES we have math-common/cos.cl, while in generic
SOURCES it is math/cos.cl. Based on current check rule that compares
both folder name and base filename, target math-common/cos.cl won't
override math/cos.cl when collecting source files from SOURCES files in
cmake function libclc_configure_lib_source.
With this PR, we allow folder name to be different in the process.
A notable change of this PR is that two entries in SOURCES with the same
base filename must not implements the same built-in.
77fe6aaeaa