travis: add test for compilation with higher optimization.

This can give more warnings, so we should test it.  Bad for debugging,
though.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

.travis.yml

@@ -7,6 +7,7 @@ notifications:
 
 env:
   - ARCH=32 SOURCE_CHECK_ONLY=true
+  - ARCH=64 SOURCE_CHECK_ONLY=true CDEBUGFLAGS="-std=gnu11 -g -fstack-protector -O3 -flto" LDFLAGS="-O3 -flto"
   - VALGRIND=0 ARCH=32 DEVELOPER=1 COMPILER=gcc TEST_GROUP=1 TEST_GROUP_COUNT=2 SOURCE_CHECK_ONLY=false
   - VALGRIND=0 ARCH=32 DEVELOPER=1 COMPILER=gcc TEST_GROUP=2 TEST_GROUP_COUNT=2 SOURCE_CHECK_ONLY=false
   - VALGRIND=0 ARCH=64 DEVELOPER=1 COMPILER=gcc SOURCE_CHECK_ONLY=false