Merge pull request #5394 from Mousius/optimize-bgemv #1392

Job	Run time
TEST (LA464, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA464)	7m 49s
TEST (LOONGSON3R5, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSON3R5)	14m 38s
TEST (LOONGSON2K1000, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSON2K1000)	15m 31s
TEST (DYNAMIC_ARCH, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=GENERIC)	7m 45s
TEST (LA64_GENERIC, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA64_GENERIC)	14m 59s
TEST (LA264, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA264)	8m 32s
TEST (LOONGSONGENERIC, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSONGENERIC)	8m 22s
	1h 17m 36s

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