Define DBX_REGISTER_NUMBER for IA MCU

Since IA MCU uses the same debug register map as Linux/x86, we copy
DBX_REGISTER_NUMBER together with TARGET_ASM_FILE_START_FILE_DIRECTIVE
and ASM_COMMENT_START from i386/gnu-user.h to i386/iamcu.h.

	* config/i386/iamcu.h (TARGET_ASM_FILE_START_FILE_DIRECTIVE):
	New.  Copied from config/i386/gnu-user.h.
	(ASM_COMMENT_START): Likewise.
	(DBX_REGISTER_NUMBER): Likewise.

From-SVN: r226363

gcc/ChangeLog

+2015-07-29  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* config/i386/iamcu.h (TARGET_ASM_FILE_START_FILE_DIRECTIVE):
+	New.  Copied from config/i386/gnu-user.h.
+	(ASM_COMMENT_START): Likewise.
+	(DBX_REGISTER_NUMBER): Likewise.
+
 2015-07-29  Richard Biener  <rguenther@suse.de>
 
 	* gimple-fold.c (fold_gimple_cond): Remove.

gcc/config/i386/iamcu.h

@@ -26,6 +26,17 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #undef TARGET_SUBTARGET_DEFAULT
 #define TARGET_SUBTARGET_DEFAULT MASK_IAMCU
 
+/* Output at beginning of assembler file.  */
+/* The .file command should always begin the output.  */
+#define TARGET_ASM_FILE_START_FILE_DIRECTIVE true
+
+#undef ASM_COMMENT_START
+#define ASM_COMMENT_START "#"
+
+#undef DBX_REGISTER_NUMBER
+#define DBX_REGISTER_NUMBER(n) \
+  (TARGET_64BIT ? dbx64_register_map[n] : svr4_dbx_register_map[n])
+
 #undef ASM_SPEC
 #define ASM_SPEC "--32 -march=iamcu"