Add to RunCMake.Syntax test \-escape cases

Add an Escape1 test case covering \-escape cases inside bracket, quoted,
and unquoted arguments.  Also cover comments immediately after quoted
and unquoted arguments on lines containing \# escapes.

Tests/RunCMake/Syntax/Escape1-stderr.txt

@@ -0,0 +1,3 @@
+^\\##\[\[#\]\]#\[\[\]\]x#\\"
+\$\@\^\\; 	\(\)#\\"
+\$\@\^; 	\(\)$

Tests/RunCMake/Syntax/Escape1.cmake

@@ -0,0 +1,3 @@
+message([[\#]] \#[[ \#]] "#[[]]" x#comment
+  "\#\\\"\n\$\@\^\;\ \t\(\)"#comment
+   \#\\\"\n\$\@\^\;\ \t\(\))

Tests/RunCMake/Syntax/RunCMakeTest.cmake

@@ -39,6 +39,7 @@ run_cmake(BracketNoSpace2)
 run_cmake(BracketNoSpace3)
 run_cmake(BracketNoSpace4)
 run_cmake(BracketNoSpace5)
+run_cmake(Escape1)
 run_cmake(ParenNoSpace0)
 run_cmake(ParenNoSpace1)
 run_cmake(ParenNoSpace2)