Disable C compiler warnings entirely

[serebit]

Description

In Meson 1.4.0, warnings for Vala-transpiled C code were unhidden, which causes the Budgie build to turn into unreadable logspam due to the absolutely abysmal C code generated by Vala. This PR restores the prior behavior by disabling all warnings for C code.

Let it be known that I didn't want to have to do this and would have fixed the code myself. If I could have.

Submitter Checklist

• [x] Squashed commits with git rebase -i (if needed)
• [x] Built budgie-desktop and verified that the patch worked (if needed)

[JoshStrobl]

@serebit Now it triggers the following:

../src/daemon/tabswitcher.vala:64:38: error: implicit declaration of function ‘xfw_window_x11_get_xid’; did you mean ‘wnck_window_get_xid’? [-Wimplicit-function-declaration]

So still need those it seems