Update Makefile for macOS

Update Makefile for macOS

Changes to deal with compilation (particularly profile-build) on macOS.
(1) The default toolchain has gcc masquerading as clang,
    the previous Makefile was not picking up the required changes
    to the different profiling tools.
(2) The previous Makefile test for gccisclang occurred before
    a potential overwrite of CXX by COMPCXX
(3) llvm-profdata no longer runs as a command on macOS and
    instead is invoked by ``xcrun llvm-profdata``
(4) Needs to support use of true gcc using e.g.
    ``make build ... COMPCXX=g++-10``
(5) enable profile-build in travis for macOS

closes https://github.com/official-stockfish/Stockfish/pull/3043

No functional change