>From gcc(1):
-ffile-prefix-map=old=new
[...] Specifying this option is equivalent to specifying all the
individual -f*-prefix-map options. This can be used to make reproducible
builds that are location independent.
Specifically, this additionally enables -fmacro-prefix-map=, which causes
prefix mapping to be applied to expansions of __FILE__ and similar macros.
Without this option, if source files are compiled by passing the
absolute file path to the compiler (as done by e.g. cmake), any
expansions of __FILE__ (e.g. from uses of assert()) will contain
$srcdir.
Signed-off-by: Allan McRae <allan@archlinux.org>
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