stest_rfp: STFSM test is very sensitive to small numeric errors in BLAS STRSM

[martin-frbg]

As originally reported in https://github.com/xianyi/OpenBLAS/issues/3648 , the test for STFSM in sdrvrf3.f compares against the result of STRSM with a fairly small default threshold. While this happens to work with the reference implementation of the BLAS, spurious failure may occur with a user-supplied BLAS (as observed with OpenBLAS) although the deviation is within the expectations for a single precision calculation making use of FMA or similar hardware features. While this situation is more or less described in the FAQ as a "minor testing failure" (http://www.netlib.org/lapack/faq.html#_how_do_i_interpret_lapack_testing_failures) it may be causing unnecessary concern for distribution packagers etc. Suggested options would be to compare against DTRSM, or trivially to increase the threshold. The same (non?)issue very likely exists with ctest_rfp/CTFSM