Created attachment 1930744 [details] giac-alloca-c99.patch It appears that in micropython, mpconfigport.h is responsible for including <alloca.h> or equivalent. In the bundled copy, micropython-1.12/xcas/mpconfigport.h has the include directive commented out. This results in an implicit declaration. There is another issue in the bundled quickjs code: It seems that <fenv.h> is not included for fesetround (still need to investigate that). I'll try to report these issues on the upstream forum.
Regarding the fesetround issue, there is a stray fenv.h file (with incompatible definitions) in the source tree.
Created attachment 1930761 [details] Remove <fenv.h> override This patch is required to remove the <fenv.h> override. The build now succeeds. I think I'm going to push this in the light of the breakage reported in bug 2150422. It seems a reasonable cleanup. Upstream forum account has still not been activated.
Looks like I won't get upstream forum access, so the patch remains downstream-only.