Add curly brackets to list of characters that gn needs to escape

tools/gn/escape_unittest.cc

Index: tools/gn/escape_unittest.cc
diff --git a/tools/gn/escape_unittest.cc b/tools/gn/escape_unittest.cc
index f2b2eae19742e1451b17a5126d8710cf85275f1c..fc7692d2da29c641a3c38cb77ab2c3a1c36f2613 100644
--- a/tools/gn/escape_unittest.cc
+++ b/tools/gn/escape_unittest.cc
@@ -49,6 +49,10 @@ TEST(Escape, PosixCommand) {
 
   // Some more generic shell chars.
   EXPECT_EQ("a_\\;\\<\\*b", EscapeString("a_;<*b", opts, nullptr));
+
+  // Curly braces must be escaped to avoid brace expansion on systems using
+  // bash as default shell..
+  EXPECT_EQ("\\{a,b\\}\\{c,d\\}", EscapeString("{a,b}{c,d}", opts, nullptr));
 }
 
 TEST(Escape, NinjaPreformatted) {