[C++] Protect call to copy_attributes_to_builtin (PR91505)

[C++] Protect call to copy_attributes_to_builtin (PR91505)

copy_attributes_to_builtin only handles BUILT_IN_NORMAL, but C++ was
calling it immediately after the:

	  if (DECL_BUILT_IN_CLASS (newdecl) == BUILT_IN_NORMAL)

block.  The corresponding C code calls it inside the block instead.

2019-08-21  Richard Sandiford  <richard.sandiford@arm.com>

gcc/cp/
	PR c++/91505
	* decl.c (duplicate_decls): Call copy_attributes_to_builtin inside
	the BUILT_IN_NORMAL block rather than afterward.

gcc/testsuite/
	PR c++/91505
	* g++.target/i386/crc32-4.C: New test.

From-SVN: r274799