Mark symbols as constant

Mark symbols as constant

Aarch64_legitimate_constant_p currently returns false for symbols,
eventhough they are always valid constants.  This means LOSYM isn't
CSEd correctly.  If we return true CSE works better, resulting in
smaller/faster code (0.3% smaller code on SPEC2006).  Avoid this
for TLS symbols since their sequence is complex.

    gcc/
	* config/aarch64/aarch64.c (aarch64_legitimate_constant_p):
	Return true for non-tls symbols.

From-SVN: r249442