Removing race condition when compiling for OptiX 7

[cmstein]

Description

This removes a race condition when compiling PTX device code in a multithreaded environment.

The problems stems from OptiX6 requiring the rend_lib.cu device bitcode to be linked to each compiled shadergroup whereas we only need to link the rend_lib.cu device bitcode to one shadergroup in OptiX7. When I added OptiX7 support, I put a static/global in OSL to ensure that we don't get multiple definitions from rend_lib.cu in the device code for OptiX7. But that's a poor solution for a couple of reasons:

• it's not thread-safe
• it doesn't support recompiling shaders in an interactive environment.

This removes the requirement to supply the rend_lib.cu device code when using OptiX7. But that also means the renderer now needs to manually link it in. Both testshade and testrender have been updated to reflect this.

Tests

testsuite runs the same with this fix

Checklist:

• I have read the contribution guidelines.
• I have previously submitted a Contributor License Agreement.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[lgritz]

LGTM, and it passed testsuite for me by hand as well.