Make the inlines static to avoid kernel build failure with Clang 11 on i386.
(The issue was not observed with Clang 10, currently in tree; reproduction
depends on compiler inlining choices.)
The compiler may choose not to inline 'bare' C inlines, and in that case
expects a symbol of the same name will be available. It does not
automatically define that symbol at use, because of traditional C linking
semantics. (In contrast, C++ does define it, and then deduplicates redundant
definitions at link). As we do not instantiate the C99 inline ('extern
inline ...;'), the linker errors with "undefined symbol."
Reported by: dim
Tested by: dim
Fixes: r364219
03a2f473c5