* gdb.arch/i386-prologue.c: Add copyright header. Use preprocessor

	* gdb.arch/i386-prologue.c: Add copyright header.  Use preprocessor
	directives to conditionalize symbol prefixing.
	* gdb.arch/i386-prologue.exp: Allow symbol prefixing by adding
	additional_flags handling.  Add underscore prefix for Cygwin.
	* gdb.arch/i386-unwind.c: Use preprocessor directives to
	conditionalize symbol prefixing.
	* gdb.arch/i386-unwind.exp: Allow symbol prefixing by adding
	additional_flags handling.  Add underscore prefix for Cygwin.