[SR-9016] Multiline string literals not quite working in directives

[dabrahams]

Previous ID	SR-9016
Radar	None
Original Reporter	@dabrahams
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: bba9dee0eadbdfddf6981636ca1786ee

Issue Description:

Run this:

@available(*, deprecated, message:
    """
    This is a message \
    that has only one line \
    written on multiple lines
    """)
var x = 3
var y = x

print(
    """
    This is a message \
    that has only one line \
    written on multiple lines
    """)

Note how the output of the print differs from that of the warning:

x.swift:8:9: warning: 'x' is deprecated: 
    This is a message     that has only one line     written on multiple lines
    
var y = x
        ^
This is a message that has only one line written on multiple lines

[belkadan]

Fixed in master by @johnno1962! #19219