[compiler-rt] Make MaybeReexec properly process DYLD_INSERT_LIBRARIES when using non-absolute paths

MaybeReexec() in asan_mac.cc checks for presence of the ASan dylib in DYLD_INSERT_LIBRARIES, and if it is there, it will process this env. var. and remove the dylib from its value, so that spawned children don't have this variable set. However, the current implementation only works when using a canonical absolute path to the dylib, it fails to remove the dylib for example when using @executable_path.

This patch changes the processing of DYLD_INSERT_LIBRARIES to comparing values only based on filenames (ignoring directories).

Reviewed at http://reviews.llvm.org/D7160

llvm-svn: 228392