Merge pull request #5399 from Mousius/bgemm-8x4 #1718

Job	Run time
TEST (DYNAMIC_ARCH=1, TARGET=RISCV64_GENERIC BINARY=64 ARCH=riscv64 DYNAMIC_ARCH=1, rv64,g=true,c...	7m 1s
TEST (RISCV64_ZVL128B, TARGET=RISCV64_ZVL128B BINARY=64 ARCH=riscv64, rv64,g=true,c=true,v=true,v...	7m 2s
TEST (RISCV64_ZVL256B, TARGET=RISCV64_ZVL256B BINARY=64 ARCH=riscv64, rv64,g=true,c=true,v=true,v...	6m 38s
	20m 41s

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