Enable pthread_equal function definition (WebAssembly#374)

Author: shengyun-zhou

Makefile

@@ -251,6 +251,7 @@ LIBC_TOP_HALF_MUSL_SOURCES += \
         thread/pthread_condattr_setpshared.c \
         thread/pthread_create.c \
         thread/pthread_detach.c \
+        thread/pthread_equal.c \
         thread/pthread_getspecific.c \
         thread/pthread_join.c \
         thread/pthread_key_create.c \

expected/wasm32-wasi-pthread/defined-symbols.txt

@@ -1297,12 +1297,6 @@ pthread_condattr_setpshared
 pthread_create
 pthread_detach
 pthread_equal
-pthread_exit
-pthread_getattr_default_np
-pthread_getattr_np
-pthread_getconcurrency
-pthread_getcpuclockid
-pthread_getschedparam
 pthread_getspecific
 pthread_join
 pthread_key_create
@@ -1616,8 +1610,6 @@ thrd_create
 thrd_current
 thrd_detach
 thrd_equal
-thrd_exit
-thrd_join
 thrd_sleep
 thrd_yield
 time