optimise dot using thread throttling for NEOVERSE V1 #5600

Job	Run time
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 24s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	2m 37s
neoverse_build	8m 30s
build (ubuntu-latest, gfortran, make)	21m 35s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 38s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	2m 39s
build (ubuntu-latest, gfortran, cmake)	44m 52s
build (ubuntu-latest, flang, make)	18m 29s
build (ubuntu-latest, flang, cmake)	43m 46s
msys2 (CLANG64, int32, Release)	16m 59s
msys2 (MINGW32, int32, Release)	17m 26s
msys2 (UCRT64, int32, Release)	16m 4s
build (macos-latest, gfortran, cmake)	27m 41s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	13m 52s
msys2 (CLANG64, int64, Release)	17m 28s
msys2 (UCRT64, int64, Release)	14m 50s
build (macos-latest, gfortran, make)	11m 14s
	4h 45m 4s

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