gdb, symtab: inline find_quick_global_symbol_language

gdb, symtab: inline find_quick_global_symbol_language

There is only one use of find_quick_global_symbol_language that calls it
for the special symbol "main".

Inline the function as it is probably not correct in the general case
where we may have multiple instances of global symbols with the same name
but different languages in different libraries in different linker
namespaces.

Further, change the objfiles iteration into a call to
gdbarch_iterate_over_objfiles_in_search_order, which would only search the
initial linker namespace, where we expect "main" to be located.