MFH: r430465 r430466 r430467 r430475 r430615 r432608 r432640

Move forward to 5.0-gtk3 release.
Changes: http://rawtherapee.com/blog/rawtherapee-5-released

Fix compilation on FreeBSD 11+, and enable OpenMP.
Use devel/openmp for libomp.

Code generation improvements: On i386, use SSE2 instead of only SSE [1]
when compiler optimizations are requested (which they are by default) RT
code uses mostly SSE2 for SIMD). Fix i386 SSE2 crashes with GCC(*) (use
clang there), and clean up a bit.

(*) GCC does not get the stack properly aligned in i386 for SSE2 and
causes SIGBUS on startup when trying to access an 8-byte aligned
double[8] array with SIMD instructions. One workaround is -mstackrealign
(which RT does on Win32), the other is to use clang - we don't get
OpenMP on i386 anyhow, so clang 3.4 in 10.3 is sufficient.

Drop -fexpensive-optimizations, clang does not support it, and gcc 5.4
includes it in -O2 and -O3.

Note that the upstream discourages the use of 32-bit architectures for
rawtherapee.

Approved by: ports-secteam@ (junovitch)