[bug-diffutils] bug#48062: make check fails if configured with --program-prefix

[Jun T]

$ ./configure --program-prefix=g
$ make
$ make check

then two tests diff3 and help-version fail.
The reason is quite simple; the log contains lines like

+diff3: subsidiary program 'gdiff' not found

If I run

$ cd src
$ ln -s diff gdiff

then 'make check' succeeds.

If there were a program named 'gdiff' in my PATH then it would
have been used for the test.