[Support/Unix] Unconditionally include time.h.

[Support/Unix] Unconditionally include time.h.

When building LLVM on Linux with libc++ with CMake TIME_WITH_SYS_TIME is
undefined, and HAVE_SYS_TIME_H is defined. This ends up including
sys/time.h but not time.h. Unix/TimeValue.inc requires time.h for asctime_r
and localtime. libstdc++ seems to include time.h anyway, but libc++ does
not.

Fix this by always including time.h

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155382 91177308-0d34-0410-b5e6-96231b3b80d8