run-pass/const-endianness: negate before to_le()
run-pass/const-endianness: negate before to_le()

`const LE_I128` needs parentheses to negate the value *before* calling
`to_le()`, otherwise it doesn't match the operations performed in the
black-boxed part of the test.  This only makes a tangible difference on
big-endian targets.

GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust