Spell "calling convention" out in full.

We only use this in one other place anyway.

Also be explicit about how `__tls_get_addr` and `___tls_get_addr` differ, since I missed that at first!

Change-Id: Ica214886c5346f118f063bca26e6dd8d74ee21f4
diff --git a/libc/private/bionic_elf_tls.h b/libc/private/bionic_elf_tls.h
index 3a7b381..8bd5bc5 100644
--- a/libc/private/bionic_elf_tls.h
+++ b/libc/private/bionic_elf_tls.h
@@ -214,14 +214,14 @@
 };
 
 #if defined(__i386__)
-#define TLS_GET_ADDR_CCONV __attribute__((regparm(1)))
+#define TLS_GET_ADDR_CALLING_CONVENTION __attribute__((regparm(1)))
 #define TLS_GET_ADDR ___tls_get_addr
 #else
-#define TLS_GET_ADDR_CCONV
+#define TLS_GET_ADDR_CALLING_CONVENTION
 #define TLS_GET_ADDR __tls_get_addr
 #endif
 
-extern "C" void* TLS_GET_ADDR(const TlsIndex* ti) TLS_GET_ADDR_CCONV;
+extern "C" void* TLS_GET_ADDR(const TlsIndex* ti) TLS_GET_ADDR_CALLING_CONVENTION;
 
 struct bionic_tcb;
 void __free_dynamic_tls(bionic_tcb* tcb);