Fix references to HAVE_PRCTL.

Change-Id: I8343b398f2ce0d743487fdd086e67763c7dd67f1
diff --git a/libutils/Threads.cpp b/libutils/Threads.cpp
index 9bcd063..b2c6903 100644
--- a/libutils/Threads.cpp
+++ b/libutils/Threads.cpp
@@ -35,7 +35,7 @@
 # define HAVE_CREATETHREAD  // Cygwin, vs. HAVE__BEGINTHREADEX for MinGW
 #endif
 
-#if defined(HAVE_PRCTL)
+#if defined(__linux__)
 #include <sys/prctl.h>
 #endif
 
@@ -100,7 +100,7 @@
 };
 
 void androidSetThreadName(const char* name) {
-#if defined(HAVE_PRCTL)
+#if defined(__linux__)
     // Mac OS doesn't have this, and we build libutil for the host too
     int hasAt = 0;
     int hasDot = 0;