Using gputils r681, building from source in a separate build directory fails, as gpasm.h.in (and later several other .h.in files) are not found.
To reproduce, issue the following commands in the source directory of gputils (next to ChangeLog):
$ mkdir build
$ cd build
$ ../configure --prefix=$HOME/local
The attached file fixes this, by having make locate the input files.
Apply next to ChangeLog via
patch -p0 < fix-out-of-tree-builds.patch