Use nqp::fc instead of nqp::lc and add a test

Added test did not pass before this and the previous commit had been made.

Author: samcv

src/vm/moar/QAST/QASTRegexCompilerMAST.nqp

@@ -1000,7 +1000,7 @@ class QAST::MASTRegexCompiler {
         }
         elsif $node.list && $node.subtype eq 'ignorecase' {
             my $lit := $!regalloc.fresh_s();
-            nqp::push(@ins, op('const_s', $lit, sval(nqp::lc($node[0]))));
+            nqp::push(@ins, op('const_s', $lit, sval(nqp::fc($node[0]))));
             unless nqp::existskey(%!reg, 'haystacklc') {
                 %!reg<haystacklc> := $!regalloc.fresh_s();
             }

t/qregex/rx_modifiers

@@ -1,4 +1,5 @@
 ##  modifiers
+:i st			st	y	ignorecase with ligature st (:i)
 :i bcd			abcdef	y	ignorecase (:i)
 :i bcd			aBcdef	y	ignorecase (:i)
 :i bcd			abCdef	y	ignorecase (:i)