function and struct should not have same declaration name

[gSahitya-samsung]

stdlib.h and signal.h in os/include using same struct and function name i.e. mallinfo & sigaction. The function declaration shadows the struct declaration resulting in build warnings. The PR #6585 has been raised to prevent warnings to come during build, but proper fix is needed.

The proper fix can be as follow:

1. Either change struct or function name
2. Move functions declaration into separate header file

Reference - https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html