Shorten compiler flags when developing.
Shorten compiler flags when developing.

This commit attempts to make it easier to read build output, and
hopefully makes configure.ac easier as well.

-Wall has already been added around line 645, no need to add it twice.

On GCC -Wreturn-type is a part of -Wall, which we enable elsewhere.

    https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

On Clang -Wreturn-type is enabled by default:

    https://clang.llvm.org/docs/DiagnosticsReference.html#wreturn-type

Same with -Wswitch as -Wreturn-type, so that can be removed as well.

Finally, use spaces instead of tabs to make cc output shorter and more
readable.

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache