Fix Tcl quoting in gdb_assert

The gdb_assert proc under-quotes the expression that is passed in.
This leads to weird code in a couple of spots that tries to
compensate:

    gdb_assert {{$all_regs eq $completed_regs}} ...

The fix is to add a bit of quoting when evaluating the expression.

gdb/testsuite/gdb.base/completion.exp

@@ -159,7 +159,7 @@ foreach {-> reg} [regexp -all -inline -line {^info registers (\w+\S*)} $regs_out
     lappend completed_regs $reg
 }
 set completed_regs [join [lsort $completed_regs]]
-gdb_assert {{$all_regs eq $completed_regs}} "complete 'info registers '"
+gdb_assert {$all_regs eq $completed_regs} "complete 'info registers '"
 
 # Tests below are about tab-completion, which doesn't work if readline
 # library isn't used.  Check it first.

gdb/testsuite/gdb.base/step-over-no-symbols.exp

@@ -76,9 +76,9 @@ proc test_step_over { displaced } {
 
     set after_addr [get_pc "get after PC"]
 
-    gdb_assert {{[regexp "^${hex}$" $before_addr] \
-		 && [regexp "^${hex}$" $after_addr] \
-		 && $before_addr != $after_addr}} "advanced"
+    gdb_assert {[regexp "^${hex}$" $before_addr] \
+		    && [regexp "^${hex}$" $after_addr] \
+		    && $before_addr != $after_addr} "advanced"
 }
 
 foreach displaced { "off" "on" "auto" } {

gdb/testsuite/lib/gdb.exp

@@ -1942,7 +1942,7 @@ proc gdb_assert { condition {message ""} } {
 	set message $condition
     }
 
-    set code [catch {uplevel 1 expr $condition} res]
+    set code [catch {uplevel 1 [list expr $condition]} res]
     if {$code == 1} {
 	# If code is 1 (TCL_ERROR), it means evaluation failed and res contains
 	# an error message.  Print the error message, and set res to 0 since we