add support for macOS

[s-u]

This is a minimal set of code changes and additions to cmake rules to allow flang and libpgmath to build on macOS (aka Darwin).

[Tested using clang6 to build on Darwin 15.6.0 (aka OS X 10.11.6)]

[gklimowicz]

Simon, can you do an individual contributor license agreement for us so we can take this pull request?

NVIDIA is requiring that we do CLAs for this sort of outside contribution.

This is described in the Flang wiki here: https://github.com/flang-compiler/flang/wiki/Community

[gklimowicz]

@s-u FYI, I can't take these changes without a completed contributor license agreement. At least for about another few weeks.

If you have an update for this, please let me know.

[kiranchandramohan]

@s-u CLA (contributor license agreement) is not a requirement now. If you are interested in submitting this PR please rebase, else consider closing.

[s-u]

@kiranchandramohan thanks, rebased and updated.
I have tested the build using classic-flang-llvm-project (bootstrapped with Xcode 10.3) on macOS 10.14 (Mojave) = Darwin 18.

[pawosm-arm]

Seems like each time I thought I was approving particular commit, it was approval for the entire PR!

[pawosm-arm]

The commit message user fileno() instead of direct structure access is about fileno() only, yet the commit additionally sorts out dumpregs()/getRegs() definitions. This is considered as lame behavior, consider splitting this commit in two, or update the commit message to reflect correctly the scope of the change.

[dnoan]

runtime/flangrti/CMakeLists.txt has FLANG_LIBOMP and LIBPGMATH hard-coded to libomp.so and libpgmath.so. These should be set to libomp.dylib and libpgmath.dylib on Mac. Otherwise the project doesn't compile.

[kiranchandramohan]

@s-u Can you address @dnoan's comment above?

Also could you let me know the build instructions you used for Mac?

[s-u]

Build instruction are like in the Wiki only slightly modified - your mileage may wary depending on tools used.

BASE="`pwd`"
CMAKE=/Applications/CMake.app/Contents/bin/cmake

INSTALL_PREFIX=/opt/flang
CMAKE_OPTIONS="-DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX \
    -DLLVM_CONFIG=$INSTALL_PREFIX/bin/llvm-config \
    -DCMAKE_CXX_COMPILER=$INSTALL_PREFIX/bin/clang++ \
    -DCMAKE_C_COMPILER=$INSTALL_PREFIX/bin/clang \
    -DCMAKE_Fortran_COMPILER=$INSTALL_PREFIX/bin/flang 
    -DCMAKE_Fortran_COMPILER_ID=Flang \
    -DCMAKE_BUILD_TYPE=Release \
    -DLLVM_TARGETS_TO_BUILD=X86"

cd classic-flang-llvm-project
mkdir -p build && cd build
## There is a bug in that branch that uses wrong flags for xml2 so we have to disable it
$CMAKE $CMAKE_OPTIONS -DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang++ \
       -DLLVM_ENABLE_CLASSIC_FLANG=ON -DLLVM_ENABLE_PROJECTS="clang;openmp;libcxx;libcxxabi" \
       -DLLVM_ENABLE_LIBXML2=OFF ../llvm
make -j12

cd "$BASE"

(cd flang/runtime/libpgmath
 mkdir -p build && cd build
 $CMAKE $CMAKE_OPTIONS ..
 make -j12
 make install)

(cd flang
 mkdir -p build && cd build
 $CMAKE $CMAKE_OPTIONS -DFLANG_LLVM_EXTENSIONS=ON \
	-DFLANG_LIBOMP=$INSTALL_PREFIX/lib/libomp.dylib -DLIBPGMATH=$INSTALL_PREFIX/lib/libpgmath.dylib ..
 make -j12
 make install)

@dnoan it says that those are undefined, so if you define them it works, no code change needed. I have now added a fix for the suffixes as well (so now you no longer need to set those).