[gdb/build] Fix struct token odr violation

When building gdb with -O2 -flto I run into:
...
/data/vries/gdb/src/gdb/c-exp.y:2450:8: warning: type 'struct token' \
  violates the C++ One Definition Rule [-Wodr]
 struct token
        ^
/data/vries/gdb/src/gdb/d-exp.y:939:8: note: a different type is defined in \
  another translation unit
 struct token
        ^
...

Fix this by renaming to c_token and d_token.

Likewise in:
- fortran-exp.y, renaming to f_token,
- go-exp.y, renaming to go_token, and
- p-exp.y, renaming to p_token.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

PR build/22395
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=22395