(SC_PATH_TKCONFIG): Don't exit 0 if tkconfig fails.
(SC_LOAD_TCLCONFIG): Quote all uses of TCL_BIN_DIR, it may contain
"# no Tcl configs found".
(SC_LOAD_TKCONFIG): Similarily for TK_BIN_DIR.
* gdb/configure.ac (gdbkt): Check both no_tcl/no_tk first, before
doing any further tcl/tk configury. Don't configure gdbtk if
tcl or tk check fails.
* gdb/aclocal.m4: Regenerate.
* gdb/configure: Regenerate.
* gdb/gdbtk/plugins/aclocal.m4: Regenerate.
* gdb/gdbtk/plugins/configure: Regenerate.
