THRIFT-1462 add more strict compiler flags

Patch: Roger Meier
diff --git a/lib/cpp/Makefile.am b/lib/cpp/Makefile.am
index 4bd40fb..668af0a 100755
--- a/lib/cpp/Makefile.am
+++ b/lib/cpp/Makefile.am
@@ -47,7 +47,7 @@
 pkgconfig_DATA += thrift-qt.pc
 endif
 
-AM_CXXFLAGS = -Wall
+AM_CXXFLAGS = -Wall -Wextra -pedantic
 AM_CPPFLAGS = $(BOOST_CPPFLAGS) -I$(srcdir)/src
 AM_LDFLAGS = $(BOOST_LDFLAGS)