erofs-utils: improve compatibility and reduce header conflicts

erofs-utils: improve compatibility and reduce header conflicts

Adjust initializers of union in erofs-utils to ensure compatibility
with various compilers. The original C99 designated initializer style
was not supported in other compilers (e.g., C++11), leading to build
failures.  Additionally, change the codebase to minimize potential
conflicts with headers from other projects.

Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240624063217.170251-1-hongzhen@linux.alibaba.com
[ Gao Xiang: minor commit message update. ]
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>