Fortran: host association issue with symbol in COMMON block [PR108454]

When resolving a flavorless symbol that is already registered with a COMMON
block, and which neither has the intrinsic, generic, or external attribute,
skip searching among interfaces to avoid false resolution to a derived type
of the same name.

	PR fortran/108454

gcc/fortran/ChangeLog:

	* resolve.cc (resolve_common_blocks): Initialize variable.
	(resolve_symbol): If a symbol is already registered with a COMMON
	block, do not search for an interface with the same name.

gcc/testsuite/ChangeLog:

	* gfortran.dg/common_29.f90: New test.