MINOR: tools: ease the declaration of known symbols in resolve_sym_name()

MINOR: tools: ease the declaration of known symbols in resolve_sym_name()

Let's have a macro that declares both the symbol and its name, it will
avoid the risk of introducing typos, and encourages adding more when
needed. The macro also takes an optional second argument to permit an
inline declaration of an extern symbol.

(cherry picked from commit a3582a77f73a1c2ba84018ac361b4a763582ac44)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 2a9991d23f5ba6d60c725fed3f0705c9b18bdd15)
Signed-off-by: Willy Tarreau <w@1wt.eu>