Silence -Wcast-qual warnings showing up with newer version of g++.

Somewhen between gcc 11 and a 14 pre-release, g++ started to complain about the C-style casts: subprocess.h: In function ‘int subprocess_create_ex(const char* const*, int, const char* const*, subprocess_s*)’: subprocess.h:877:27: warning: cast from type ‘const char* const*’ to type ‘char* const*’ casts away qualifiers [-Wcast-qual] 877 | (char *const *)commandLine, used_environment)) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~ The pragmas for clang should not be needed anymore.