Operating system: Arch Linux
Graphics card: RX 580
Broken: df1e9b662bd6938f74579cea9d30341f3b6dd02b, "Cleanup: Fix build warnings from OSL shader compilation"
Worked: 6a28d14f7236b3e6fbe7409da9ee916878d65feb, "Fix T73740: Auto-key "Only Available" de-selects f-curves"
Short description of error
Blender cannot find "stdosl.h", even though it exists.
Exact steps for others to reproduce the error
On Arch Linux, install openshadinglanguage, and then attempt to compile Blender master.
Upon examining the borked commit, I noticed this comment:
FindOSL.cmake does not give us the location of the shader library but generally it can be figured out from the location of the oslc compiler. However if this fails you can set OSL_SHADER_DIR to bypass the auto discovery.
Unfortunately, there is no provided CMake option allowing a custom OSL_SHADER_DIR location to be set, as the current assumptions don't account for where packagers may place system files. In Arch Linux, the compiler is here, "/usr/bin/oslc", while the shader directory is here, "/usr/share/OSL/shaders".