Clean up __isthreaded.

__isthreaded is annoying for ARC++ and useless for everyone. Just hard-code
the value in ndk_cruft for LP32 and be done with it.

Bug: N/A
Test: builds
Change-Id: I08f11a404bbec55ed57cb1e18b5116163c7d7d13
diff --git a/libc/bionic/ndk_cruft.cpp b/libc/bionic/ndk_cruft.cpp
index 016b476..dbacf18 100644
--- a/libc/bionic/ndk_cruft.cpp
+++ b/libc/bionic/ndk_cruft.cpp
@@ -52,6 +52,9 @@
 // LP64 doesn't need to support any legacy cruft.
 #if !defined(__LP64__)
 
+// By the time any NDK-built code is running, there are plenty of threads.
+int __isthreaded = 1;
+
 // These were accidentally declared in <unistd.h> because we stupidly used to inline
 // getpagesize() and __getpageshift(). Needed for backwards compatibility with old NDK apps.
 unsigned int __page_size = PAGE_SIZE;