[LLD][ELF] - ICF: add test case testing we do not fold sections with the different flags. NFCI.

Previously the following condition was not tested at all:
https://github.com/llvm-mirror/lld/blob/master/ELF/ICF.cpp#L300

Patch adds a test for `A->Flags != B->Flags` part.

llvm-svn: 338375