[MacPorts] #57612: clang does not respect -syslibroot when linking

[MacPorts]

#57612: clang does not respect -syslibroot when linking
---------------------+--------------------
  Reporter:  kencu   |      Owner:  (none)
      Type:  defect  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:
      Port:          |
---------------------+--------------------

Comment (by kencu):

 `macports-clang-7.0`, at least, works just the same as Xcode 10's clang
 1000+.
 {{{
 $ clang++ -v -Wl,-v -Wl,-syslibroot
 -Wl,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk
 -o hello  hello.o
 clang version 7.0.0 (tags/RELEASE_700/final)
 Target: x86_64-apple-darwin18.2.0
 Thread model: posix
 InstalledDir: /opt/local/libexec/llvm-7.0/bin
  "/opt/local/libexec/llvm-7.0/bin/ld" -demangle -lto_library
 /opt/local/libexec/llvm-7.0/lib/libLTO.dylib -dynamic -arch x86_64
 -macosx_version_min 10.14.0 -syslibroot
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk
 -o hello -v -syslibroot
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk
 hello.o -lc++ -lSystem
 /opt/local/libexec/llvm-7.0/lib/clang/7.0.0/lib/darwin/libclang_rt.osx.a
 @(#)PROGRAM:ld  PROJECT:ld64-409.12
 BUILD 17:47:51 Sep 25 2018
 configured to support archs: armv6 armv7 armv7s arm64 i386 x86_64 x86_64h
 armv6m armv7k armv7m armv7em arm64e arm64_32
 Library search paths:
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/lib
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/lib
 Framework search paths:
         /Library/Frameworks/
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/
 }}}

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Ticket URL: <https://trac.macports.org/ticket/57612#comment:12>
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