[MacPorts] #58493: cctools: using clang < 5.0 as default assembler generates assembly errors in some cases

[MacPorts]

#58493: cctools: using clang < 5.0 as default assembler generates assembly errors
in some cases
----------------------+----------------------
  Reporter:  kencu    |      Owner:  jeremyhu
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:
Resolution:           |   Keywords:
      Port:  cctools  |
----------------------+----------------------

Comment (by kencu):

 clang-3.7 fails:
 {{{
 $ clang-mp-3.7 -arch i386 testasm.S
 ld: in section __TEXT,__text reloc 0: unsupported r_length=0 for scattered
 vanilla reloc file '/var/folders/I0/I0fOotq3ErGZHYxrmmWiqU+++TI/-Tmp
 -/testasm-dad071.o' for architecture i386
 clang: error: linker command failed with exit code 1 (use -v to see
 invocation)
 }}}
 but clang-3.8 and newer are fine:
 {{{
 $ clang-mp-3.8 -arch i386 testasm.S
 Undefined symbols for architecture i386:
   "_main", referenced from:
       start in crt1.10.6.o
 ld: symbol(s) not found for architecture i386
 clang: error: linker command failed with exit code 1 (use -v to see
 invocation)
 }}}
 {{{
 $ clang-mp-5.0 -arch i386 testasm.S
 Undefined symbols for architecture i386:
   "_main", referenced from:
       start in crt1.10.6.o
 ld: symbol(s) not found for architecture i386
 clang: error: linker command failed with exit code 1 (use -v to see
 invocation)
 }}}
 this is as expected, as clang-3.8 is about Apple's clang 800.

 I will update the clang blacklisting in the gcc portfiles to match,
 because clang-9.0 can't build gcc (a different error, to be in a different
 ticket) and we need some proper fallbacks available.

-- 
Ticket URL: <https://trac.macports.org/ticket/58493#comment:34>
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