doc: Convert mingw-w64.org links to https

gcc:
	* doc/install.texi (Binaries): Convert mingw-w64.org to https.
	(Specific): Ditto.

Author: GeraldPfeifer

gcc/doc/install.texi

@@ -3473,7 +3473,7 @@ Microsoft Windows:
 The @uref{https://sourceware.org/cygwin/,,Cygwin} project;
 @item
 The @uref{https://osdn.net/projects/mingw/,,MinGW} and
-@uref{http://www.mingw-w64.org/,,mingw-w64} projects.
+@uref{https://www.mingw-w64.org/,,mingw-w64} projects.
 @end itemize
 
 @item
@@ -5080,7 +5080,7 @@ the Win32 subsystem that provides a subset of POSIX.
 
 @subheading Intel 64-bit versions
 GCC contains support for x86-64 using the mingw-w64
-runtime library, available from @uref{http://mingw-w64.org/doku.php}.
+runtime library, available from @uref{https://mingw-w64.org/doku.php}.
 This library should be used with the target triple x86_64-pc-mingw32.
 
 Presently Windows for Itanium is not supported.