[Build] Reduce amount of warnings

[lbonn]

Remove some warnings which pop up when building rofi and hide real issues when developing

• one unused parameter in recursivebrowser.c
• overlength strings are overly pedantic, modern compilers support large strings
• __FUNCTION__ creeped back in after warning: ISO C does not support #288

What's left:

• non conformant cast in libgwater

../subprojects/libgwater/xcb/libgwater-xcb.c:160:35: warning: ISO C forbids conversion of object pointer to function pointer type [-Wpedantic]
  160 |     g_source_set_callback(source, (GSourceFunc)(void *)callback, user_data, destroy_func);

• unchecked return values (always write(), dmenu.c and recursivebrowser.c)

../source/modes/dmenu.c:309:19: warning: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  309 |                   write(pd->pipefd2[1], "r", 1);