[OpenMP] Don't link libm with -Wl,--as-needed on FreeBSD

[jbeich]

Summary

-Wl,--as-needed omits libm when building with BFD linker (e.g., from GNU binutils 2.32). Affects FreeBSD 11.* amd64/armv6/i386, 12.0 armv6/i386 (where LLD is not default yet).

Fixes https://bugs.llvm.org/show_bug.cgi?id=32279

$ LDFLAGS=-fuse-ld=bfd cmake .
$ make libomp-micro-tests
[...]
ld: error: runtime/src/libomp.so: undefined reference to scalbnl
ld: error: runtime/src/libomp.so: undefined reference to fmaxl
ld: error: runtime/src/libomp.so: undefined reference to logbl
ld: error: runtime/src/libomp.so: undefined reference to scalbnf
ld: error: runtime/src/libomp.so: undefined reference to scalbn

[dim]

LGTM from a FreeBSD point of view. :)

[AndreyChurbanov]

LGTM

[jbeich]

Can someone land D68045, D68051 (this review), D68053? I didn't test on non-FreeBSD because contributing guide didn't cover how to.

[AndreyChurbanov]

Jan,
you may want to ask for D68045 landing there directly, as compiler-rt is a different project which I don't work on.

openmp/runtime/cmake/LibompHandleFlags.cmake

 # Library flags
 function(libomp_get_libflags libflags)
   set(libflags_local)
   libomp_append(libflags_local "${CMAKE_THREAD_LIBS_INIT}")
   libomp_append(libflags_local "${LIBOMP_HWLOC_LIBRARY}" LIBOMP_USE_HWLOC)
   if(${IA32})
     libomp_append(libflags_local -lirc_pic LIBOMP_HAVE_IRC_PIC_LIBRARY)
   endif()
-  if(${CMAKE_SYSTEM_NAME} MATCHES "DragonFly")
+  if(${CMAKE_SYSTEM_NAME} MATCHES "DragonFly|FreeBSD")
     libomp_append(libflags_local "-Wl,--no-as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
     libomp_append(libflags_local "-lm")
     libomp_append(libflags_local "-Wl,--as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
-  elseif(${CMAKE_SYSTEM_NAME} MATCHES "(Free|Net)BSD")
+  elseif(${CMAKE_SYSTEM_NAME} MATCHES "NetBSD")
     libomp_append(libflags_local -lm)
   endif()
   set(libflags_local ${libflags_local} ${LIBOMP_LIBFLAGS})
   libomp_setup_flags(libflags_local)
   set(${libflags} ${libflags_local} PARENT_SCOPE)
 endfunction()
 
 # Fortran flags