Remove Itanium support

[fingolfin]

This PR removes support for Itanium systems, as threatened in issue #1114 and the mailing lists.

[ChrisJefferson]

Without any testing, there is no value keeping this code around.

[codecov]

Codecov Report

Merging #1163 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1163      +/-   ##
==========================================
+ Coverage   68.36%   68.36%   +<.01%     
==========================================
  Files         435      435              
  Lines      230659   230659              
==========================================
+ Hits       157686   157687       +1     
+ Misses      72973    72972       -1

Impacted Files	Coverage Δ
src/gasman.c	83.85% <ø> (ø)	✅
src/compiler.c	65.5% <ø> (+0.04%)	✅

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