[PATCH] erofs-utils: fix "non-trivial designated initializers not supported"

[Gao Xiang]

This partially reverts commit 79f6e168d94c ("erofs-utils: improve
compatibility and reduce header conflicts") since some C++ compiler
will complain:

include/erofs_fs.h: In function 'void erofs_check_ondisk_layout_definitions()':
include/erofs_fs.h:460:2: sorry, unimplemented: non-trivial designated initializers not supported

Let's just bypass this compile-time check for the C++ language since
only external programs may be written by C++.

Fixes: 79f6e168d94c ("erofs-utils: improve compatibility and reduce header conflicts")
Cc: Hongzhen Luo <hongzhen at linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 include/erofs_fs.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/erofs_fs.h b/include/erofs_fs.h
index 0d603c4..fc21915 100644
--- a/include/erofs_fs.h
+++ b/include/erofs_fs.h
@@ -450,14 +450,14 @@ struct z_erofs_lcluster_index {
 /* check the EROFS on-disk layout strictly at compile time */
 static inline void erofs_check_ondisk_layout_definitions(void)
 {
+#ifndef __cplusplus
 	const union {
 		struct z_erofs_map_header h;
 		__le64 v;
 	} fmh __maybe_unused = {
-		.h = {
-			.h_clusterbits = 1 <<Z_EROFS_FRAGMENT_INODE_BIT,
-		},
+		.h.h_clusterbits = 1 << Z_EROFS_FRAGMENT_INODE_BIT,
 	};
+#endif
 
 	BUILD_BUG_ON(sizeof(struct erofs_super_block) != 128);
 	BUILD_BUG_ON(sizeof(struct erofs_inode_compact) != 32);
@@ -476,9 +476,11 @@ static inline void erofs_check_ondisk_layout_definitions(void)
 
 	BUILD_BUG_ON(BIT(Z_EROFS_LI_LCLUSTER_TYPE_BITS) <
 		     Z_EROFS_LCLUSTER_TYPE_MAX - 1);
+#ifndef __cplusplus
 	/* exclude old compiler versions like gcc 7.5.0 */
 	BUILD_BUG_ON(__builtin_constant_p(fmh.v) ?
 		     fmh.v != cpu_to_le64(1ULL << 63) : 0);
+#endif
 }
 
 #endif
-- 
2.39.3