The implicit toolchain probe includes every system header that the
runtime and vendored sources spell, under __has_include. clang ships
<riscv_vector.h> for every target, and through clang 18 including it
without the RISC-V vector extension is an #error. Since the vendored
zlib's adler32_simd.c spells it, the probe failed with clang 18, which
disabled the native cache and program sharding: a sanitized dev build
then compiled the whole program as one translation unit.
The probe now includes <riscv_vector.h> only where __riscv_vector is
defined, and the probe's header test covers it and a riscv64 target.
Chris Tate
f003bb4d68