Adjust multithreading threshold in S/DGER and add an intermediate step #5969

Job	Run time
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	12m 19s
neoverse_build	7m 43s
msys2 (CLANG64, int32, Release)	16m 29s
msys2 (MINGW32, int32, Release)	15m 43s
msys2 (CLANG64, int64, Release)	15m 39s
msys2 (UCRT64, int32, Release)	14m 21s
build (ubuntu-latest, gfortran, cmake)	52m 6s
build (macos-latest, gfortran, make)	4m 23s
build (ubuntu-latest, flang, cmake)	44m 44s
msys2 (UCRT64, int64, Release)	15m 45s
build (ubuntu-latest, gfortran, make)	25m 15s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	2m 57s
build (ubuntu-latest, flang, make)	18m 48s
build (macos-latest, gfortran, cmake)	15m 26s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 40s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	2m 57s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 19s
	4h 31m 34s

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