PL/Tcl: Don't link with -lc explicitly

PL/Tcl: Don't link with -lc explicitly

It has been reported that PL/Tcl built on macOS with GCC >=11 crashes.
The reason is that there is a hash_search() function in the operating
system's libraries, and that ends up being called instead of the one
in postgres.  This has something to do with how the linker resolves
references between the various possibilities it has been given, and
somehow something changed that it is now picking that one in this
configuration.

We found that removing the -lc from the link command line fixes this
problem.  The -lc was introduced a long time ago in commit
e3909672f12e0ddf3e202b824fda068ad2195ef2, and we think the reasons
might be obsolete, so we decided that we'll try to just remove it and
see if any problems arise.

Discussion: https://www.postgresql.org/message-id/flat/a78c847a-4f79-9286-be99-e819e9e4139e%40enterprisedb.com