middle-end: Disable section anchors for VAR_DECLs if -fdata-sections

middle-end: Disable section anchors for VAR_DECLs if -fdata-sections

-fdata-sections places data symbols into their own, unique, named sections.
-fsection-anchors create an anchor to access neighboring symbols
within a section.

When both are enabled, a separate section anchor is created for each
symbol, which provides no benefit.

This patch updates the common gating function use_blocks_for_decl_p() to
return false if -fdata-sections is enabled.

gcc/ChangeLog:

	* varasm.c (use_blocks_for_decl_p): Don't use section anchors
	for VAR_DECLs if -fdata-sections enabled.