[compiler-rt][builtins] Use c[tl]zsi macro instead of __builtin_c[tl]z

`__builtin_c[tl]z` accepts `unsigned int` argument that is not always the
same as uint32_t. For example, `unsigned int` is uint16_t on MSP430.

Reviewed By: aykevl

Differential Revision: https://reviews.llvm.org/D86547