[MacPorts] #53931: clang's ld doesn't recognise "-lto_library" flag on 10.6

[MacPorts]

#53931: clang's ld doesn't recognise "-lto_library" flag on 10.6
-------------------------+-------------------------------------------------
 Reporter:  mojca        |      Owner:  jeremyhu
     Type:  defect       |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:  snowleopard  |       Port:  clang-3.9 clang-4.0 llvm-3.9
                         |  llvm-4.0
-------------------------+-------------------------------------------------
 See [https://build.macports.org/builders/ports-10.6_x86_64_legacy-
 builder/builds/25698 this failed build] for example. This is clang 3.9
 failing to build llvm 4.0 on Snow Leopard:

 {{{
   /opt/local/bin/clang-mp-3.9 -pipe -Os -arch x86_64
   -mmacosx-version-min=10.6 -Wl,-search_paths_first
   -Wl,-headerpad_max_install_names -L/opt/local/lib
   -Wl,-headerpad_max_install_names
   CMakeFiles/cmTC_25d4d.dir/testCCompiler.c.o -o cmTC_25d4d

   ld: library not found for -lto_library

   clang: error: linker command failed with exit code 1 (use -v to see
   invocation)
 }}}

 Joshua suggested:
 > Looks like `ld` is interpreting `-lto_library` as `-l` with a library
 name of `to_library`. No LTO support I guess.

 I didn't test clang 3.8, but clang 3.7 works on 10.6 and clang 4.0 works
 on 10.7.

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Ticket URL: <https://trac.macports.org/ticket/53931>
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