Better workaround for builtins #75

Job	Run time
Native build	7s
Cross build (ia64-unknown-linux-gnu)	27m 13s
Cross build (alpha-unknown-linux-gnu)	23m 15s
Cross build (x86_64-unknown-linux-gnu)	23m 50s
Cross build (i386-unknown-linux-gnu)	23m 6s
Cross build (arm-unknown-linux-gnueabi)	23m 5s
Cross build (arm-unknown-linux-gnueabihf)	23m 1s
Cross build (hppa-unknown-linux-gnu)	22m 34s
Cross build (aarch64-unknown-linux-gnu)	25m 5s
Cross build (mips-unknown-linux-gnu)	23m 47s
Cross build (mipsel-unknown-linux-gnu)	24m 35s
Cross build (powerpc-unknown-linux-gnu)	23m 8s
Cross build (s390-unknown-linux-gnu)	22m 55s
Cross build (s390x-unknown-linux-gnu)	23m 4s
Cross build (sparc-unknown-linux-gnu)	23m 16s
Cross build (powerpc64le-unknown-linux-gnu)	23m 59s
Cross build (mips64el-unknown-linux-gnuabi64)	23m 46s
	6h 19m 46s

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