DOCS, pybench : Add build notes for Windows and flang from gh Discussion 5008 #5161

Job	Run time
build (ubuntu-latest, gfortran, cmake)	41m 53s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	5m 43s
build (ubuntu-latest, gfortran, make)	16m 43s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	10m 3s
build (ubuntu-latest, flang, cmake)	12m 46s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	5m 28s
build (ubuntu-latest, flang, make)	7m 11s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	5m 6s
build (macos-latest, gfortran, cmake)	29m 44s
build (macos-latest, gfortran, make)	5m 52s
msys2 (UCRT64, int32, Release)	14m 48s
msys2 (UCRT64, int64, Release)	17m 11s
msys2 (MINGW32, int32, Release)	19m 50s
msys2 (CLANG64, int32, Release)	20m 16s
msys2 (CLANG64, int64, Release)	18m 5s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	16m 14s
	4h 6m 53s

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