Add aarch64-w64-mingw32 target to libgcc

Reuse MinGW definitions from i386 for libgcc. Move reused files to
libgcc/config/mingw folder.

libgcc/ChangeLog:

	* config.host: Add aarch64-w64-mingw32 target. Adjust targets
	after moving MinGW files.
	* config/i386/t-gthr-win32: Move to...
	* config/mingw/t-gthr-win32: ...here.
	* config/i386/t-mingw-pthread: Move to...
	* config/mingw/t-mingw-pthread: ...here.
	* config/aarch64/t-no-eh: New file. EH is not yet implemented for
	the target, and the default definition should be disabled.

libgcc/config.host

@@ -452,6 +452,21 @@ aarch64*-*-vxworks7*)
 	tmake_file="${tmake_file} ${cpu_type}/t-softfp t-softfp t-crtfm"
 	tmake_file="${tmake_file} t-dfprules"
 	;;
+aarch64-*-mingw*)
+	case ${target_thread_file} in
+	  win32)
+	    tmake_thr_file="mingw/t-gthr-win32"
+	    ;;
+	  posix)
+	    tmake_thr_file="mingw/t-mingw-pthread"
+	    ;;
+	esac
+	tmake_file="${tmake_file} ${cpu_type}/t-no-eh ${tmake_thr_file}"
+	tmake_file="${tmake_file} t-dfprules"
+	tmake_file="${tmake_file} ${cpu_type}/t-aarch64"
+	tmake_file="${tmake_file} ${cpu_type}/t-lse"
+	tmake_file="${tmake_file} ${cpu_type}/t-softfp t-softfp t-crtfm"
+	;;
 alpha*-*-linux*)
 	tmake_file="${tmake_file} alpha/t-alpha alpha/t-ieee t-crtfm alpha/t-linux"
 	extra_parts="$extra_parts crtfastmath.o"
@@ -870,10 +885,10 @@ i[34567]86-*-mingw*)
 	fi
 	case ${target_thread_file} in
 	  win32)
-	    tmake_thr_file="i386/t-gthr-win32"
+	    tmake_thr_file="mingw/t-gthr-win32"
 	    ;;
 	  posix)
-	    tmake_thr_file="i386/t-mingw-pthread"
+	    tmake_thr_file="mingw/t-mingw-pthread"
 	    ;;
 	  mcf)
 	    tmake_thr_file="i386/t-mingw-mcfgthread"
@@ -897,10 +912,10 @@ i[34567]86-*-mingw*)
 x86_64-*-mingw*)
 	case ${target_thread_file} in
 	  win32)
-	    tmake_thr_file="i386/t-gthr-win32"
+	    tmake_thr_file="mingw/t-gthr-win32"
 	    ;;
 	  posix)
-	    tmake_thr_file="i386/t-mingw-pthread"
+	    tmake_thr_file="mingw/t-mingw-pthread"
 	    ;;
 	  mcf)
 	    tmake_thr_file="i386/t-mingw-mcfgthread"

libgcc/config/aarch64/t-no-eh

@@ -0,0 +1,2 @@
+# Not using EH
+LIB2ADDEH =