Unable to upgrade libomp @17.0.3 -- Build Failed -- clang 3.7 missing atomic support

[RobK88]

I am unable to upgrade libomp to version @17.0.3 on Lion. During the upgrade, MacPorts installed clang-3.7 (@3.7.1_9) for the first time which appears to be missing atomic support needed to build libomp.

See attached main.log.

bash-3.2$ sudo port clean libomp
--->  Cleaning libomp
bash-3.2$ 
bash-3.2$ sudo port installed libomp
The following ports are currently installed:
  libomp @16.0.6_0+universal (active)
bash-3.2$ 
bash-3.2$ sudo port upgrade libomp
--->  Computing dependencies for libomp
--->  Fetching archive for libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://packages.macports.org/libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://ywg.ca.packages.macports.org/mirror/macports/packages/libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://mirror.fcix.net/macports/packages/libomp
--->  Fetching distfiles for libomp
--->  Verifying checksums for libomp
--->  Extracting libomp
--->  Applying patches to libomp
--->  Configuring libomp
--->  Building libomp                                    
Error: Failed to build libomp: command execution failed  
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_libomp/libomp/main.log for details.
Error: Follow https://guide.macports.org/#project.tickets if you believe there is a bug.
bash-3.2$

Workaround -- install or upgrade libomp using clang-7.0 which includes atomic support (thanks to kencu).

bash-3.2$ sudo port clean libomp
--->  Cleaning libomp
bash-3.2$ 
bash-3.2$ sudo port installed libomp
The following ports are currently installed:
  libomp @16.0.6_0+universal (active)
bash-3.2$ 
bash-3.2$ sudo port upgrade libomp configure.compiler=macports-clang-7.0
--->  Computing dependencies for libomp
--->  Fetching archive for libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://packages.macports.org/libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://ywg.ca.packages.macports.org/mirror/macports/packages/libomp
--->  Attempting to fetch libomp-17.0.3_0+universal.darwin_11.i386-x86_64.tbz2 from http://mirror.fcix.net/macports/packages/libomp
--->  Fetching distfiles for libomp
--->  Verifying checksums for libomp
--->  Extracting libomp
--->  Applying patches to libomp
--->  Configuring libomp
--->  Building libomp                                    
--->  Staging libomp into destroot                       
--->  Installing libomp @17.0.3_0+universal
--->  Cleaning libomp
--->  Deactivating libomp @16.0.6_0+universal
--->  Cleaning libomp
--->  Activating libomp @17.0.3_0+universal
--->  Cleaning libomp
--->  Scanning binaries for linking errors
--->  No broken files found.                             
--->  No broken ports found.
--->  Some of the ports you installed have notes:
  libomp has the following notes:
    To use this OpenMP library:
     * For clang-3.8+, or clang-3.7 with +openmp variant:
        add "-fopenmp" during compilation / linking.
     * For clang-3.7 without +openmp variant, use:
        "-I/opt/local/include/libomp -L/opt/local/lib/libomp -fopenmp"
bash-3.2$