declarations and definitions. These may then be referred to from Go
code as though they were defined in the package "C". All names
declared in the preamble may be used, even if they start with a
lower-case letter. Exception: static variables in the preamble may
not be referenced from Go code; static functions are permitted.

See $GOROOT/cmd/cgo/internal/teststdio and $GOROOT/misc/cgo/gmp for examples. See

	02	// There are two fields in the type (len(structType.field))
	01	// Start of first field structure; add 1 to get field number 0: field[0].name
	01	// 1 byte
	58	// structType.field[0].name = "X"
	01	// Add 1 to get field number 1: field[0].id
	04	// structType.field[0].typeId is 2 (signed int).
	00	// End of structType.field[0]; start structType.field[1]; set field number to -1.
	01	// Add 1 to get field number 0: field[1].name

Some non-simple shifts have operands in the Go assembly which don't map directly
onto operands in the PPC64 assembly. When an operand in a shift instruction in the
Go assembly is a bit mask, that mask is represented as a start and end bit in the
PPC64 assembly instead of a mask. See the ISA for more detail on these types of shifts.
Here are a few examples:

	RLWMI $7,R3,$65535,R6 	=>	rlwimi r6,r3,7,16,31