Bug#836378: perl: -fdebug-prefix-map=... shouldn't go in ccflags

[Niko Tyni]

Package: perl
Version: 5.22.2-4

Following #832179, dpkg-buildflags now include '-fdebug-prefix-map=<cwd>'
by default. This currently ends up in $Config{ccflags} too, so all XS
package builds will now get perl's build directory, which is suboptimal
if not broken.

Rebuilding libencode-perl_2.86-1 locally, I see command lines such as

 x86_64-linux-gnu-gcc -c  -I../Encode -D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fdebug-prefix-map=/build/perl-A2er0v/perl-5.22.2=. -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fPIE -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2   -DVERSION=\"2.04\" -DXS_VERSION=\"2.04\" -fPIC "-I/usr/lib/x86_64-linux-gnu/perl/5.22/CORE"   Byte.c

Presumably the latter correct -fdebug-prefix-map overrides the first one.

The intention is not to push dpkg-buildflags contents to $Config{ccflags},
so that packages can opt in or out of their usage independently. (Normally
they get dpkg-buildflags via debhelper anyway.) So apparently there's
something wrong with filtering dpkg-buildflags from %Config. I'll dig
into it.
-- 
Niko Tyni   ntyni at debian.org