Hello

This patch implements the TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION 
target hook for the AMD GCN architecture, such that when vectorized, 
calls to builtin standard math functions such as asinf, exp, pow etc. 
are converted to calls to the recently added vectorized math functions 
for GCN in Newlib. The -fno-math-errno flag is required in addition to 
the usual vectorization optimization flags for this to occur, and some 
of the math functions (the larger double-precision ones) require a large 
stack size to function properly.

This patch requires the GCN vector math functions in Newlib to function 
- these were included in the recent 4.3.0.20230120 snapshot. As this was 
a minimum requirement starting from the patch 'amdgcn, libgomp: Manually 
allocated stacks', this should not be a problem.

I have added new testcases in the testsuite that compare the output of 
the vectorized math functions against the scalar, passing if they are 
sufficiently close. With the testcase for standalone GCN (without 
libgomp) in gcc.target/gcn/, there is a problem since gcn-run currently 
cannot set the stack size correctly in DejaGnu testing, so I have made 
it a compile test for now - it is still useful to check that calls to 
the correct functions are being made. The runtime correctness is still 
covered by the libgomp test.

Okay for trunk?

Thanks

Kwok