匹配数量不均匀的转义符号

我需要匹配C++预处理器语句。现在,预处理器语句可能跨越多行:

#define foobar \
    "something glorious"

#define foobar \\
No longer in preprocessor.

问题是如何有效地匹配显式行延拓。我有下面的表达,我 认为

/
    [^\\]           # Something that's not an escape character, followed by …
    (?<escape>\\*?) # … any number of escapes, …
    (?P=escape)     # … twice (i.e. an even number).
    \\ \n           # Finally, a backslash and newline.
/x

(我使用的是PHP,因此PCRE规则适用,但我希望您能给出以下答案: 任何 Regex方言。)