Define mte_supported() on non-aarch64.

It turns out that we need this on non-aarch64 more than I thought
we would, so let's start defining it everywhere.

Also expose platform headers to sanitizer-status.

Bug: 135772972
Change-Id: Ia7fd8a9bca0c123c4ca2ecd5f250f3a628a5513b
diff --git a/libc/platform/bionic/mte.h b/libc/platform/bionic/mte.h
index fbf3895..1e393eb 100644
--- a/libc/platform/bionic/mte.h
+++ b/libc/platform/bionic/mte.h
@@ -31,16 +31,14 @@
 #include <sys/auxv.h>
 #include <bionic/mte_kernel.h>
 
-#ifdef __aarch64__
 inline bool mte_supported() {
-#ifdef ANDROID_EXPERIMENTAL_MTE
+#if defined(__aarch64__) && defined(ANDROID_EXPERIMENTAL_MTE)
   static bool supported = getauxval(AT_HWCAP2) & HWCAP2_MTE;
 #else
   static bool supported = false;
 #endif
   return supported;
 }
-#endif
 
 #ifdef __aarch64__
 class ScopedDisableMTE {