Hello @dancingmirrors, splitting Proton apart to its components and building them separately is not supported in general. It looks like wine's tests are disabled at https://github.com/ValveSoftware/Proton/blob/proton_10.0/Makefile.in#L430 and this is inert code.
Setting that aside, this might be from https://github.com/ValveSoftware/wine/commit/404d0d48f0f917fecb017ea4af38f3e79ca4b097#diff-cffb1a841fb4a8ec0541d39f703eaf1fd6f886525a16f5226b494d4e8c07304dR2621 missing a closing brace.
Gotcha. Since I spent a while fixing the build I'll just sum up the issues I encountered in case anybody else ever hits this: the mfplat test needed a small fixup, some _bsf code needed to be adapted for FFmpeg 7+, and OpenCL needed help to link since it only seems to be set for macOS. For seemingly unrelated reasons it was broken at runtime (imm32 I think?) so my little experiment ended there.
the missing brace is real and matches the spot kisak pointed at in 404d0d4, but the tests themselves are explicitly turned off in the proton makefile, so the file is never compiled in a normal build
that makes the failure only show up if someone forces the wine test suite on, which is outside the supported path. the report is still useful as a note for anyone who later enables those tests, but it does not affect the actual proton packages
if the goal is just a clean tree, the one-line fix is straightforward, otherwise this can stay as documentation of the disabled path
proton 10.0x1 2025-11
There appears to be a missing closing brace in tests/bcrypt.c at line 2777, so the build fails by default.