depends: always set CMAKE_POSITION_INDEPENDENT_CODE=ON

Rather than potentially having to set this per-package, set it globally,
as this should always be what we want. Without doing this, changes in
later commits will have to add this per-package.

Similar to https://github.com/bitcoin/bitcoin/pull/29488, which is the
Autotools equivalent.

depends/packages.md

@@ -163,7 +163,7 @@ From the [Gentoo Wiki entry](https://wiki.gentoo.org/wiki/Project:Quality_Assura
 >  ecosystem, as it leads to a massive number of unnecessary rebuilds.
 
 Where possible, packages are built with Position Independant Code. Either using
-the autotools `--with-pic` flag, or `DCMAKE_POSITION_INDEPENDENT_CODE` with CMake.
+the Autotools `--with-pic` flag, or `CMAKE_POSITION_INDEPENDENT_CODE` with CMake.
 
 ## Secondary dependencies: