[vault] Remove Werror from build flags. Contributes to JB#44876

Gcc 4.9 incorectly thinks tests_common.hpp string() is unused, used
via macro and template. Not necessarily the most needed method, but
since Werror will cause this sort of compiler update problems, let's
just remove that flag.

CMakeLists.txt

@@ -20,7 +20,7 @@ find_package(Qt5Core REQUIRED)
 find_package(Cor REQUIRED)
 
 set(CMAKE_CXX_FLAGS
-  "${CMAKE_CXX_FLAGS} -fPIC -W -Wall -Wextra -Werror -g -O2 -std=c++0x")
+  "${CMAKE_CXX_FLAGS} -fPIC -W -Wall -Wextra -g -O2 -std=c++0x")
 
 #-Wno-psabi is to remove next g++ warning/note:
 #the mangling of 'va_list' has changed in GCC 4.4