Fix compilation against musl lib C (#7875)

Summary:
See https://github.com/percona/PerconaFT/pull/450

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7875

Reviewed By: ajkr

Differential Revision: D25938020

Pulled By: jay-zhuang

fbshipit-source-id: 9014dbc7b23bf92c5e63bfbdda4565bb0d2f2b58

utilities/transactions/lock/range/range_tree/lib/portability/toku_pthread.h

@@ -153,7 +153,12 @@ typedef struct toku_mutex_aligned {
   { .pmutex = PTHREAD_MUTEX_INITIALIZER, .psi_mutex = nullptr }
 #endif  // defined(TOKU_PTHREAD_DEBUG)
 #else   // __FreeBSD__, __linux__, at least
+#if defined(__GLIBC__)
 #define TOKU_MUTEX_ADAPTIVE PTHREAD_MUTEX_ADAPTIVE_NP
+#else
+// not all libc (e.g. musl) implement NP (Non-POSIX) attributes
+#define TOKU_MUTEX_ADAPTIVE PTHREAD_MUTEX_DEFAULT
+#endif
 #if defined(TOKU_PTHREAD_DEBUG)
 #define TOKU_ADAPTIVE_MUTEX_INITIALIZER                                    \
   {                                                                        \