tools: Add -Werror by default to all tools/

And provide an option to ./configure to disable it.

A follow-up patch will remove -Werror from every other Makefile in
tools/.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

tools/configure.ac

@@ -81,6 +81,7 @@ m4_include([../m4/header.m4])
 AX_XEN_EXPAND_CONFIG()
 
 # Enable/disable options
+AX_ARG_DEFAULT_ENABLE([werror], [Build tools without -Werror])
 AX_ARG_DEFAULT_DISABLE([rpath], [Build tools with -Wl,-rpath,LIBDIR])
 AX_ARG_DEFAULT_DISABLE([githttp], [Download GIT repositories via HTTP])
 AX_ARG_DEFAULT_ENABLE([monitors], [Disable xenstat and xentop monitoring tools])