Add ARM EABI function __aeabi_read_tp

By default, Clang uses this arm32 function to read the thread pointer,
either for ELF TLS or via __builtin_thread_pointer(). It's probably better
to inline the cp15 access using -mtp=cp15, but that's not the default yet.

See https://reviews.llvm.org/D34878?id=114573.

Bug: http://b/78026329
Test: bionic unit tests
Change-Id: I93b8926075f0b2cea8df9ef518d54f2820a8ff5b
diff --git a/libc/Android.bp b/libc/Android.bp
index 3e607f6..01c0cad 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -760,6 +760,7 @@
                 "arch-arm/generic/bionic/strcpy.S",
                 "arch-arm/generic/bionic/strlen.c",
 
+                "arch-arm/bionic/__aeabi_read_tp.S",
                 "arch-arm/bionic/atomics_arm.c",
                 "arch-arm/bionic/__bionic_clone.S",
                 "arch-arm/bionic/_exit_with_stack_teardown.S",