[COMMITTED] Change multiprecision.org to use https

As reported at
https://gcc.gnu.org/pipermail/gcc/2022-February/238216.html,
multiprecision.org now uses https so this updates the documentation
to use https instead of http.

Committed as obvious.

gcc/ChangeLog:

	* doc/install.texi:

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index f4e7dc4..deb9938 100644 (file)
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -406,7 +406,7 @@ download_prerequisites installs.
 @item MPC Library version 1.0.1 (or later)
 
 Necessary to build GCC@.  It can be downloaded from
-@uref{http://www.multiprecision.org/mpc/}.  If an MPC source distribution
+@uref{https://www.multiprecision.org/mpc/}.  If an MPC source distribution
 is found in a subdirectory of your GCC sources named @file{mpc}, it
 will be built together with GCC.  Alternatively, if MPC is already
 installed but it is not in your default library search path, the