[libc] Fix typo in platform_defs.h.inc

Differential Revision: https://reviews.llvm.org/D87687

Author: gchatelet

libc/config/linux/platfrom_defs.h.inc renamed to libc/config/linux/platform_defs.h.inc

@@ -2,8 +2,8 @@ add_gen_header(
   common
   DEF_FILE common.h.def
   PARAMS
-    platform_defs=../../config/${LIBC_TARGET_OS}/platfrom_defs.h.inc
+    platform_defs=../../config/${LIBC_TARGET_OS}/platform_defs.h.inc
   GEN_HDR common.h
   DATA_FILES
-    ../../config/${LIBC_TARGET_OS}/platfrom_defs.h.inc
+    ../../config/${LIBC_TARGET_OS}/platform_defs.h.inc
 )