[RISC-V] Possible performance improvement in matrix multiply function in Coremark

In function in Coremark:

```
#define bit_extract(x,from,to) (((x)>>(from)) & (~(0xffffffff << (to))))

void matrix_mul_matrix_bitextract(ee_u32 N, MATRES *C, MATDAT *A, MATDAT *B) {
ee_u32 i,j,k;
for (i=0; i

Start with the Coremark matrix_mul_matrix_bitextract function and reproduce its LLVM output with -O3 -march=rv32imbc -mabi=ilp32. Compare the generated inner loop with GCC's assembly, investigate the loop-termination and bit-extraction differences, and verify any improvement against Coremark correctness and performance.

Written by the indexing model from the issue text.