[llvm-bugs] [Bug 30811] New: Unconditionally passed `-lto_library` to the linker on Darwin confused by symlinks

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30811

            Bug ID: 30811
           Summary: Unconditionally passed `-lto_library` to the linker on
                    Darwin confused by symlinks
           Product: clang
           Version: trunk
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: howarth.mailing.lists at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The change https://reviews.llvm.org/rL285254 to unconditionally pass
`-lto_library` to the linker on Darwin is confused by the use of compiler
symlinks.

This approach doesn't work if the user installs clang in a buried subdirectory
such as /sw/opt/llvm-4.0 but accesses the compilers via a /sw/bin/clang-4.0
symlink pointing at /sw/opt/llvm-4.0/bin/clang-4.0...

$ /sw/bin/clang-4.0 -flto himenoBMTxpa.c
clang-4.0: warning: libLTO.dylib relative to clang installed dir not found;
using 'ld' default search path instead [-Wliblto]
...
"/usr/bin/ld" -demangle -object_path_lto
/var/folders/vh/xthx1f251nqfj804049zl1wm0000gn/T/cc-083c59.o -no_deduplicate
-dynamic -arch x86_64 -macosx_version_min 10.11.0 -o a.out
/var/folders/vh/xthx1f251nqfj804049zl1wm0000gn/T/himenoBMTxpa-34b8ea.o -lSystem
/sw/opt/llvm-4.0/bin/../lib/clang/4.0.0/lib/darwin/libclang_rt.osx.a

$ /sw/opt/llvm-4.0/bin/clang-4.0 -flto himenoBMTxpa.c -v
...
"/usr/bin/ld" -demangle -object_path_lto
/var/folders/vh/xthx1f251nqfj804049zl1wm0000gn/T/cc-afbbef.o -lto_library
/sw/opt/llvm-4.0/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64
-macosx_version_min 10.11.0 -o a.out
/var/folders/vh/xthx1f251nqfj804049zl1wm0000gn/T/himenoBMTxpa-44b09e.o -lSystem
/sw/opt/llvm-4.0/bin/../lib/clang/4.0.0/lib/darwin/libclang_rt.osx.a

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