https://wiki.musl-libc.org/faq.html#Q:-When-compiling-something-against-musl,-I-get-error-messages-about-%3Ccode%3Esys/cdefs.h%3C/code%3E
"The bug is in the application that uses this internal glibc header. This header is not intended to be used by any program"

sys/cdefs.h does not exist in musl libc, this breaks bundled Chromium.

---
 src/3rdparty/chromium/third_party/apple_apsl/dnsinfo.h    | 8 ++++++--
 .../chromium/third_party/libsync/src/include/sync/sync.h  | 8 ++++++--
 src/3rdparty/chromium/third_party/libsync/src/sw_sync.h   | 8 ++++++--
 .../usrsctp/usrsctplib/usrsctplib/netinet/sctp_uio.h      | 8 ++++++--
 4 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/3rdparty/chromium/third_party/apple_apsl/dnsinfo.h b/src/3rdparty/chromium/third_party/apple_apsl/dnsinfo.h
index db2ad9027..4840f0ae9 100644
--- a/src/3rdparty/chromium/third_party/apple_apsl/dnsinfo.h
+++ b/src/3rdparty/chromium/third_party/apple_apsl/dnsinfo.h
@@ -91,7 +91,9 @@ typedef struct {
 #pragma pack()
 
 
-__BEGIN_DECLS
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /*
  * DNS configuration access APIs
@@ -109,6 +111,8 @@ void
 _dns_configuration_ack		(dns_config_t	*config,
 				 const char	*bundle_id);
 
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif	/* __DNSINFO_H__ */
diff --git a/src/3rdparty/chromium/third_party/libsync/src/include/sync/sync.h b/src/3rdparty/chromium/third_party/libsync/src/include/sync/sync.h
index 50ed0ac57..91dfd5d69 100644
--- a/src/3rdparty/chromium/third_party/libsync/src/include/sync/sync.h
+++ b/src/3rdparty/chromium/third_party/libsync/src/include/sync/sync.h
@@ -24,7 +24,9 @@
 
 #include <linux/types.h>
 
-__BEGIN_DECLS
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 struct sync_legacy_merge_data {
  int32_t fd2;
@@ -158,6 +160,8 @@ struct sync_pt_info *sync_pt_info(struct sync_fence_info_data *info,
                                   struct sync_pt_info *itr);
 void sync_fence_info_free(struct sync_fence_info_data *info);
 
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* __SYS_CORE_SYNC_H */
diff --git a/src/3rdparty/chromium/third_party/libsync/src/sw_sync.h b/src/3rdparty/chromium/third_party/libsync/src/sw_sync.h
index fda1c4c57..395c38072 100644
--- a/src/3rdparty/chromium/third_party/libsync/src/sw_sync.h
+++ b/src/3rdparty/chromium/third_party/libsync/src/sw_sync.h
@@ -19,7 +19,9 @@
 #ifndef __SYS_CORE_SW_SYNC_H
 #define __SYS_CORE_SW_SYNC_H
 
-__BEGIN_DECLS
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /*
  * sw_sync is mainly intended for testing and should not be compiled into
@@ -30,6 +32,8 @@ int sw_sync_timeline_create(void);
 int sw_sync_timeline_inc(int fd, unsigned count);
 int sw_sync_fence_create(int fd, const char *name, unsigned value);
 
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* __SYS_CORE_SW_SYNC_H */
diff --git a/src/3rdparty/chromium/third_party/usrsctp/usrsctplib/usrsctplib/netinet/sctp_uio.h b/src/3rdparty/chromium/third_party/usrsctp/usrsctplib/usrsctplib/netinet/sctp_uio.h
index 6298f9334..d688d9d75 100755
--- a/src/3rdparty/chromium/third_party/usrsctp/usrsctplib/usrsctplib/netinet/sctp_uio.h
+++ b/src/3rdparty/chromium/third_party/usrsctp/usrsctplib/usrsctplib/netinet/sctp_uio.h
@@ -1317,7 +1317,9 @@ sctp_sorecvmsg(struct socket *so,
  */
 #if !(defined(_KERNEL)) && !(defined(__Userspace__))
 
-__BEGIN_DECLS
+#ifdef __cplusplus
+extern "C" {
+#endif
 int	sctp_peeloff(int, sctp_assoc_t);
 int	sctp_bindx(int, struct sockaddr *, int, int);
 int	sctp_connectx(int, const struct sockaddr *, int, sctp_assoc_t *);
@@ -1355,7 +1357,9 @@ ssize_t	sctp_sendv(int, const struct iovec *, int, struct sockaddr *,
 
 ssize_t	sctp_recvv(int, const struct iovec *, int, struct sockaddr *,
 	    socklen_t *, void *, socklen_t *, unsigned int *, int *);
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif				/* !_KERNEL */
 #endif				/* !__sctp_uio_h__ */
-- 
2.35.1