tree-wide: Fix constness issues with newer glibc

tree-wide: Fix constness issues with newer glibc

Latest glibc uses _Generic to have strstr() and other functions return
const char* or char* based on whether the input is a const char* or a
char*. This causes build failures as we previously always expected a char*.

Let's fix the compilation failures and add our own macros similar to glibc's
to have string functions that return a mutable or const pointer depending on
the input.

(cherry picked from commit 0bac1ed2422f15308414dd1e9d09812a966b0348)
(cherry picked from commit 1a2e23b88734ec4be3af2eca651ec75a56161c5f)