Is /app/perl a directory? I usually unpack a perl tarball then rename the directory to the perl version number that I just unpacked as the installation prefix. For example:

mv /opt/perl444-27-O1-5.20.0-RC1 /opt
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perl444 stands for perl using gcc-4.4.4; the 27 represents the OS which is the 2.6.27 kernel; O1((that's capital O followed by 1) stands for the optimization flag that I will use; lastly, the version number which I'm using. Next, you probably should set the path for your compiler and its library:

export CC=/opt/444/bin/gcc
export LD_LIBRARY_PATH=/usr/local/lib
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Then change directory:

cd /opt/perl444-27-O1-5.20.0-RC1
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Now, following Corion's advice:

./Configure -Dcc=/opt/444/bin/gcc -Dprefix=/opt/perl444-27-O0-5.20.0-R
+C1 -DDEBUGGING
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Hit Enter and it starts the configuration.