Large Refactor of CMake build system
This commit improves numerous functionalities of the OpenMP CMake build
system to be more conducive with LLVM's build system and build philosophies.
The CMake build system, as it was before this commit, was not up to LLVM's
standards and did not implement the configuration stage like most CMake based
build systems offer (check for compiler flags, libraries, etc.) In order to
improve it dramatically in a short period of time, a large refactoring had
to be done.
The main changes done with this commit are as follows:
- Compiler flag checks - The flags are no longer grabbed from compiler specific directories. They are checked for availability in config-ix.cmake and added accordingly inside LibompHandleFlags.cmake.
- Feature checks were added in config-ix.cmake. For example, the standard CMake module FindThreads is probed for the threading model to use inside the OpenMP library.
- OS detection - There is no longer a LIBOMP_OS variable, OS-specifc build logic is wrapped around the WIN32 and APPLE macros with !(WIN32 OR APPLE) meaning a Unix flavor of some sort.
- Got rid of vestigial functions/macros/variables
- Added new libomp_append() function which is used everywhere to conditionally or undconditionally append to a list
- All targets have the libomp prefix so as not to interfere with any other project
- LibompCheckLinkerFlag.cmake module was added which checks for linker flags specifically for building shared libraries.
- LibompCheckFortranFlag.cmake module was added which checks for fortran flag availability.
- Removed most of the cruft from the translation between the perl+Makefile based build system and this one. The remaining components that they share are perl scripts which I'm in the process of removing.
There is still more left to do. The perl scripts still need to be removed, and
a config.h.in file (or similarly named) needs to be added with #cmakedefine lines
in it. But this is a much better first step than the previous system.
Differential Revision: http://reviews.llvm.org/D10656