[runtime] Disable KMP_HAVE_QUAD on NetBSD gcc

Disable KMP_HAVE_QUAD when building via gcc on NetBSD system,
as the build fails due to unimplemented builtins:

  .../kmp_atomic.cpp.o: In function `__kmpc_atomic_cmplx16_mul':
  .../kmp_atomic.cpp:1332: undefined reference to `__multc3'
  .../kmp_atomic.cpp.o: In function `__kmpc_atomic_cmplx16_div':
  .../kmp_atomic.cpp:1334: undefined reference to `__divtc3'
  ...

Differential Revision: https://reviews.llvm.org/D55478

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@348886 91177308-0d34-0410-b5e6-96231b3b80d8