Improve flang-new identification and add CI job for it on OSX-x86_64 #5385

Job	Run time
build (ubuntu-latest, gfortran, cmake)	45m 31s
build (ubuntu-latest, gfortran, make)	21m 26s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	5m 46s
build (ubuntu-latest, flang, cmake)	12m 20s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	5m 23s
build (ubuntu-latest, flang, make)	7m 6s
build (macos-latest, gfortran, cmake)	32m 11s
msys2 (UCRT64, int32, Release)	17m 3s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	6m 1s
build (macos-latest, gfortran, make)	4m 4s
msys2 (UCRT64, int64, Release)	15m 35s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	4m 48s
msys2 (MINGW32, int32, Release)	20m 38s
neoverse_build	7m 5s
msys2 (CLANG64, int32, Release)	21m 28s
msys2 (CLANG64, int64, Release)	17m 14s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	16m 52s
	4h 20m 31s

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