[android] Enable Thread tests were possible.

Enable most of the Thread test for Android. The only tests that cannot
pass right now are the ones related to backtraces, which do not use the
Linux API backtrace and would need an specific implementation.

And while Android did not get pthread_getname_np until API 26, the low
level prctl(PR_GET_NAME) works with the same restriction as in Linux
(only 15 characters). With that change, the test about thread names also
passes in Android.

Author: drodriguez

CoreFoundation/Base.subproj/CFPlatform.c

@@ -35,6 +35,10 @@
 
 #endif
 
+#if TARGET_OS_ANDROID
+#include <sys/prctl.h>
+#endif
+
 #if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_EMBEDDED_MINI || DEPLOYMENT_TARGET_WINDOWS
 #define kCFPlatformInterfaceStringEncoding	kCFStringEncodingUTF8
 #else
@@ -1416,7 +1420,18 @@ CF_CROSS_PLATFORM_EXPORT int _CFThreadSetName(_CFThreadRef thread, const char *_
 CF_CROSS_PLATFORM_EXPORT int _CFThreadGetName(char *buf, int length) {
 #if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_EMBEDDED_MINI
     return pthread_getname_np(pthread_self(), buf, length);
-#elif DEPLOYMENT_TARGET_LINUX
+#elif TARGET_OS_ANDROID
+    // Android did not get pthread_getname_np until API 26, but prctl seems to
+    // return at most 15 chars of the name + null terminator.
+    char *buffer[16] = {0};
+    if (prctl(PR_GET_NAME, buffer, 0, 0, 0) != 0) {
+        return -1;
+    }
+    size_t sz = MIN(strnlen(buffer, 15), length - 1);
+    memcpy(buf, buffer, sz);
+    buf[sz] = 0;
+    return 0;
+#elif TARGET_OS_LINUX
     return pthread_getname_np(pthread_self(), buf, length);
 #endif
     return -1;
@@ -1452,4 +1467,3 @@ CF_CROSS_PLATFORM_EXPORT void *_CFReallocf(void *ptr, size_t size) {
 }
 
 #endif
-