MINOR: tools: resolve main() only once in resolve_sym_name()

MINOR: tools: resolve main() only once in resolve_sym_name()

resolv_sym_name() calls dladdr(main) for each symbol in order to compare
the first address with other symbols. But this is pointless and quite
expensive in outputs to "show profiling" for example. Let's just keep a
local copy and have a variable indicating if the resolution is needed/
in progress/done to save the value for subsequent calls.

(cherry picked from commit a205a91bb3daa8a84fa6b429c13d39563add950f)
Signed-off-by: Willy Tarreau <w@1wt.eu>