dr_set_sve_vector_length is not exported, causing link errors when used from libdynamorio

[derekbruening]

Quoting from #6544 (comment)

All standalone decode/encode functions should be available in libdynamorio. Looking at dr_set_sve_vector_length() and dr_get_sve_vector_length() in encode_api.h: they are missing DR_API specifiers and this is why they are not exported when in a shared library.

This has now broken our internal build with PR #6544 adding a call to dr_set_sve_vector_length to raw2trace:

ld: error: undefined reference...: dr_set_sve_vector_length        

[derekbruening]

There also seems to be no test of either API routine?

[derekbruening]

Adding a call to one of these from ir_aarch64.c immediately reproduces the problem:

suite/tests/api/ir_aarch64.c:6931: undefined reference to `dr_get_sve_vector_length'

[derekbruening]

Also, the set routine returns null, but says it will not work if on an SVE system: how does the user know A) whether on an SVE system and B) whether the set routine succeeded? Should it return a bool instead?

[derekbruening]

I'm adding this test, but it seems it may fail on actual SVE hardware. I'll leave updating it as future work as I'm not sure how to detect the SVE hardware. I think the set routine should return a bool.

[derekbruening]

Re-assigning to get the test to work on SVE hardware. My suggestion is to have the set routine return a bool as well.