Build failure with -Werror=lto-type-mismatch (LTO)

This was reported on Gentoo at https://bugs.gentoo.org/878987, and I've verified that it still happens with the latest v0.3.23.

The -Wlto-type-mismatch flag warns about type mismatches in global declarations from different compilation units. The "lto" part is because those mismatches are dangerous in the presence of LTO, and the warnings are enabled by default with -flto. Adding -Werror=lto-type-mismatch moreover turns them into errors, so that said code cannot sneak into an LTO build. To reproduce, set CFLAGS="-flto -Werror=lto-type-mismatch" and build OpenBLAS.

For background, on Gentoo, users are likely to set CFLAGS="-flto" globally and then add CFLAGS+=" -Werror=lto-type-mismatch" as a safety net against miscompiled packages. On such a machine OpenBLAS will fail to build. As one of the maintainers, I could disable LTO wholesale, but of course it would be preferable (if not to difficult) to just fix the mismatches.

Reproduce the OpenBLAS build with CFLAGS="-flto -Werror=lto-type-mismatch" as described in the issue, then inspect the compiler diagnostics for mismatched global declarations across compilation units. Trace each reported declaration to the relevant C sources and verify that the build succeeds with the flags once the mismatches are resolved.