Pre-built binaries for specific versions of Solaris are available at http://sunfreeware.com/ -- be absolutely sure to get a version for your exact version of Solaris, as a gcc installation is very tightly coupled to the Solaris header files, which tend to "evolve" between OS versions. Any of the gcc binaries at this site may be used to build Tcl/Tk and all of the C-based extensions. A more recent version of gcc (such as 2.95.3) is suggested for C++ extensions, which one would build from source using an older gcc binary.
Also, ActiveTcl and Tclkit. As fond as CL is of sunfreeware.com's history, for example, he strongly favors ActiveTcl or Tclkit over Tcl things now found at sunfreeware.com.
Also, "tclsh is /usr/sfw/bin/tclsh8.4 in s10_72 ... [and] Tk is included with Solaris and has been for quite some time in package SUNWTk", Dave Uhring helpfully points out in regard to "the optional software distribution".