Move shared native target specific code to gdb/nat

https://sourceware.org/gdb/wiki/Common describes the following
directory structure:

 gdb/nat/
   Native target backend files. Code that interfaces with the
   host debug API. E.g., ptrace code, Windows debug API code,
   procfs code should go here.

 gdb/target/
   Host-independent, target vector specific code (target_ops).

 gdb/common/
   All other shared code.

This commit moves all native target backend files currently in
gdb/common to gdb/nat.

gdb/
2014-06-20  Gary Benson  <gbenson@redhat.com>

	* common/gdb_thread_db.h: Moved to nat.  All includes updated.
	* common/glibc_thread_db.h: Likewise.
	* common/i386-cpuid.h: Likewise.
	* common/i386-gcc-cpuid.h: Likewise.
	* common/linux-btrace.h: Likewise.
	* common/linux-osdata.h: Likewise.
	* common/linux-procfs.h: Likewise.
	* common/linux-ptrace.h: Likewise.
	* common/mips-linux-watch.h: Likewise.
	* common/linux-btrace.c: Moved to nat.
	* common/linux-osdata.c: Likewise.
	* common/linux-procfs.c: Likewise.
	* common/linux-ptrace.c: Likewise.
	* common/mips-linux-watch.c: Likewise.
	* nat/gdb_thread_db.h: Moved from common.
	* nat/glibc_thread_db.h: Likewise.
	* nat/i386-cpuid.h: Likewise.
	* nat/i386-gcc-cpuid.h: Likewise.
	* nat/linux-btrace.c: Likewise.
	* nat/linux-btrace.h: Likewise.
	* nat/linux-osdata.c: Likewise.
	* nat/linux-osdata.h: Likewise.
	* nat/linux-procfs.c: Likewise.
	* nat/linux-procfs.h: Likewise.
	* nat/linux-ptrace.c: Likewise.
	* nat/linux-ptrace.h: Likewise.
	* nat/mips-linux-watch.c: Likewise.
	* nat/mips-linux-watch.h: Likewise.
	* Makefile.in (HFILES_NO_SRCDIR): Reflect new locations.
	(object file files): Reordered.
	* gdb/copyright.py (EXCLUDE_LIST): Reflect new location
	of glibc_thread_db.h.

gdb/gdbserver/
2014-06-20  Gary Benson  <gbenson@redhat.com>

	* Makefile.in (SFILES): Update locations for files moved
	from common to nat.
	(object file files): Reordered.

gdb/testsuite/
2014-06-20  Gary Benson  <gbenson@redhat.com>

	* gdb.arch/i386-avx.exp: Fix include file location.
	* gdb.arch/i386-sse.exp: Likewise.

gdb/copyright.py

@@ -171,7 +171,7 @@ def main ():
 #
 # Filenames are relative to the root directory.
 EXCLUDE_LIST = (
-    'gdb/common/glibc_thread_db.h',
+    'gdb/nat/glibc_thread_db.h',
     'gdb/CONTRIBUTE',
     'gdb/gnulib/import'
 )