Comment 26 for bug 173890

Instead of adding the -d option to dpkg-buildpackage you can do the following command before anything else (this installs the required dependencies).

sudo apt-get build-dep flashplugin-nonfree

That downloads and installs all of the dependencies for the flash plugin (including development dependencies).

So the corrected instructions would be:

sudo apt-get build-dep flashplugin-nonfree
wget http://launchpadlibrarian.net/10756602/flashplugin-nonfree_9.0.115.0ubuntu2.tar.gz
tar -zxvf flashplugin-nonfree_9.0.115.0ubuntu2.tar.gz
cd flashplugin-nonfree-9.0.115.0ubuntu2
dpkg-buildpackage -b -rfakeroot

Of course, you could just install the compiled package I built http://launchpadlibrarian.net/10804892/flashplugin-nonfree_9.0.115.0ubuntu2_amd64.deb (attached to my December 8th comment), but I just said that you might not consider it good practice to install packages from an untrusted source (especially referring to the Ubuntu Forums malicious code incident)- not that you don't trust me.

Ramos, I believe your issue is that you don't have the appropriate compiling tools installed. The modified instructions I gave should fix your problem, if not, install the package build-essential in Synaptic or via command line (sudo apt-get install build-essential).