[libc] newheadergen: created sys folder for yaml files, make appropriate updates to CMake file for sys folder (#98693)

Moved sys yaml files into the sys folder.
After CMake patch lands, will make appropriate changes to account for
yaml, header, and .h.def files that are located within the sys folder in
a separate patch.

Author: RoseZhang03

libc/newhdrgen/yaml/sys_auxv.yaml renamed to libc/newhdrgen/yaml/sys/sys_auxv.yaml

@@ -1,6 +1,4 @@
 header: sys-auxv.h
-standards: 
-  - GNUExtensions
 macros: []
 types: []
 enums: []