Properly handle uninitialized common symbolhjl/pr65780/master

Uninitialized common symbol behavior in executables is target and linker
dependent.  default_binds_local_p_3 is made public and updated to take an
argument to indicate if common symbol may be local.  If common symbol
may be local, default_binds_local_p_3 will treat non-external variable
as defined locally.  default_binds_local_p_2 is changed to treat common
symbol as local for non-PIE binaries.

For i386, common symbol is local only for non-PIE binaries.  For x86-64,
common symbol is local only for non-PIE binaries or linker supports copy
reloc in PIE binaries.  If a target treats common symbol as local only
for non-PIE binaries, it can define TARGET_BINDS_LOCAL_P as
default_binds_local_p_2.

gcc/

	PR target/65780
	* output.h (default_binds_local_p_3): New.
	* varasm.c (default_binds_local_p_3): Make it public.  Take an
	argument to indicate if common symbol may be local.  If common
	symbol may be local, treat non-external variable as defined
	locally.
	(default_binds_local_p_2): Pass !flag_pic to default_binds_local_p_3.
	(default_binds_local_p_1): Pass false to default_binds_local_p_3.
	* config/i386/i386.c (ix86_binds_local_p): New.
	(TARGET_BINDS_LOCAL_P): Replace default_binds_local_p_2 with
	ix86_binds_local_p.

gcc/testsuite/

	PR target/65780
	* gcc.dg/pr65780-1.c: New test.
	* gcc.dg/pr65780-2.c: Likewise.
	* gcc.target/i386/pr32219-9.c: Likewise.
	* gcc.target/i386/pr32219-1.c (xxx): Make it initialized common
	symbol.
	* gcc.target/i386/pr64317.c (c): Initialize.

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