tools/gn: Add out-of-line copy ctors for complex classes.

tools/gn/pattern.cc

Index: tools/gn/pattern.cc
diff --git a/tools/gn/pattern.cc b/tools/gn/pattern.cc
index 4b14d2aae5251fdf3cd3a6be0eaf252aab7be9d1..3de96a3f55d717e1a6b5eb020d343f80d530e818 100644
--- a/tools/gn/pattern.cc
+++ b/tools/gn/pattern.cc
@@ -60,6 +60,8 @@ Pattern::Pattern(const std::string& s) {
        subranges_[1].type == Subrange::LITERAL);
 }
 
+Pattern::Pattern(const Pattern& other) = default;
+
 Pattern::~Pattern() {
 }
 
@@ -151,6 +153,8 @@ bool Pattern::RecursiveMatch(const std::string& s,
 PatternList::PatternList() {
 }
 
+PatternList::PatternList(const PatternList& other) = default;
+
 PatternList::~PatternList() {
 }