https://bugs.gentoo.org/898866
From: Brahmajit Das <brahmajit.xyz@gmail.com>
Date: Sat, 17 Jun 2023 15:32:10 +0000
Subject: [PATCH 1/1] Fix building against musl C library

PTHREAD_RWLOCK_PREFER_WRITER_NP isn't available in musl libc/non-glibc
systems. Checking for only __linux__ being defined isn't enough,
additional check of __GLIBC__ being defined is needed.

Signed-off-by: Brahmajit Das <brahmajit.xyz@gmail.com>
--- a/lib/FXReadWriteLock.cpp
+++ b/lib/FXReadWriteLock.cpp
@@ -80,7 +80,7 @@ FXReadWriteLock::FXReadWriteLock(){
   FXASSERT(sizeof(data)>=sizeof(pthread_rwlock_t));
   pthread_rwlockattr_t rwlockatt;
   pthread_rwlockattr_init(&rwlockatt);
-#if defined(__linux__)
+#if defined(__linux__) && defined(__GLIBC__)
   pthread_rwlockattr_setkind_np(&rwlockatt,PTHREAD_RWLOCK_PREFER_WRITER_NP);
 #endif
   pthread_rwlock_init((pthread_rwlock_t*)data,&rwlockatt);
-- 
2.41.0