refactor(declarations): also generate prototypes for functions in headers

Before this change, "static inline" functions in headers needed to have
their function attributes specified in a completely different way. The
prototype had to be duplicated, and REAL_FATTR_ had to be used instead
of the public FUNC_ATTR_ names.

TODO: need a check that a "header.h.inline.generated.h" file is not
forgotten when the first "static inline" function with attributes
is added to a header (they would just be silently missing).

test/unit/formatc.lua

@@ -264,6 +264,7 @@ local function formatc(str)
         -- and ';' indicates we're at the end of a statement, so we put end
         -- it with a newline.
         token[1] = ';\n'
+        end_at_brace = false
       end
     elseif typ == 'whitespace' then
       -- replace all whitespace by one space