Use backslash escape, replacing xargs -0 in test macro-multiline.c

[hubert.reinterpretcast]

Summary

xargs supports escaping of newline characters with backslash. xargs -0 is neither part of POSIX nor the LSB.

This patch removes the -0 option and adjusts the input to xargs accordingly; that is, the input is a text file not ending in an incomplete line, and the newline of interest is preceded by a backslash.

Note: The treatment of escaped newline characters is not as clearly specified by POSIX as for escaped blank characters; however, the same can be said for escaped backslashes. It is slightly more clear for the case where the -I option is used; however, -I is also of limited portability.

[hubert.reinterpretcast]

Ping

[bruno]

LGTM

test/Preprocessor/macro-multiline.c

-// RUN: printf -- "-DX=A\nTHIS_SHOULD_NOT_EXIST_IN_THE_OUTPUT" | xargs -0 %clang -E %s | FileCheck -strict-whitespace %s
+// RUN: printf -- "-DX=A\\\\\nTHIS_SHOULD_NOT_EXIST_IN_THE_OUTPUT\n" | xargs %clang -E %s | FileCheck -strict-whitespace %s
 
 // Per GCC -D semantics, \n and anything that follows is ignored.
 
 // CHECK: {{^START A END$}}
 START X END