add level3 defaults for x86 #5981

Job	Run time
build (ubuntu-latest, gfortran, cmake)	44m 32s
build (macos-latest, gfortran, cmake)	22m 6s
build (macos-latest, gfortran, make)	6m 39s
neoverse_build	7m 43s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	4m 33s
build (ubuntu-latest, flang, make)	18m 55s
build (ubuntu-latest, gfortran, make)	21m 31s
build (ubuntu-latest, flang, cmake)	44m 29s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	3m 29s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	4m 20s
msys2 (MINGW32, int32, Release)	13m 43s
msys2 (UCRT64, int32, Release)	43m 50s
msys2 (UCRT64, int64, Release)	44m 26s
msys2 (CLANG64, int32, Release)	1h 11m 33s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	3m 51s
msys2 (CLANG64, int64, Release)	1h 11m 41s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	42m 27s
	7h 49m 48s

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