The linker does not create symbols for static functions so Rust FFI
can't find them. All static inline function have been changed to 'inline'
functions with an 'extern inline' declaration in the corresponding .c
files. Other than Rust FFI seeing the functions this has other
advantages. See [1] for a nice explanation.
[1]
https://gustedt.wordpress.com/2010/11/29/myth-and-reality-about-inline-in-c99/