Bug#1080206: Update on bug 1080206 -- slow build time on riscv

[陈 晟祺 <harry-chen@outlook.com>]

Final update: 3.5.3-2 now compiles on riscv64 (after 10.5 hours).
Thanks for your fix!

Actually dh_auto_test takes huge portion of the time, not build:

  3/163 Test #3: cpu-cnn-inference-f32-cpp ............................... Passed 618.30 sec
 47/163 Test #47: test_convolution_backward_data_f32 ...................... Passed 782.94 sec
 48/163 Test #48: test_convolution_backward_weights_f32 ................... Passed 882.83 sec
 49/163 Test #49: test_convolution_eltwise_forward_f32 .................... Passed 939.80 sec
 51/163 Test #51: test_convolution_forward_f32 ............................ Passed 738.59 sec
 75/163 Test #75: test_pooling_backward ................................... Passed 971.11 sec
 76/163 Test #76: test_pooling_forward .................................... Passed 1437.43 sec
 91/163 Test #91: test_gemm_f32 ........................................... Passed 1040.12 sec
 92/163 Test #92: test_gemm_s8s8s32 ....................................... Passed 1085.10 sec
 94/163 Test #94: test_gemm_u8s8s32 ....................................... Passed 1077.55 sec
153/163 Test #153: test_graph_unit_dnnl_mqa_decomp_usm_cpu ................. Passed 3172.69 sec
159/163 Test #159: test_graph_unit_dnnl_sdp_decomp_usm_cpu ................. Passed 7159.01 sec

These add up to about five hours or more. I’ll disable dh_auto_test on riscv64
in the next releases until testing time becomes reasonable.

And still looking forward to your fix to enable LTO on riscv64.

Thanks,
Shengqi Chen