Fix 1 missing dependency in Makefile.in

[Torbjörn Granlund]

Vemake Vemake <vemakereporter at gmail.com> writes:

  Hi, I've fixed 1 missing dependency reported.
  This issue can cause incorrect results when gmp is incrementally built.
  Detailed speaking, any changes in the target "libtool" will not cause
  "dummy.lo" to be rebuilt, which is incorrect.
  I've tested it on my computer, the fixed version worked as expected.
  The fixed Makefile.in is attached.

Unfortunately, Makefile.in is a generated file, so any changes to it
will be overwritten.

If there is indeed a missing dependency, it ether out to be added to
Makefile.am or by means of configure.in or automake.

-- 
Torbjörn
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