do not use __float128 on non-intel platforms

[brownj85]

Context:
Aliasing of type __float128 was resulting in build failures on aarch64. This is because the GCC
extension that provides this type is not available on aarch64.

Description of the Change:
Adds a compiler check in permanent.hpp to prevent aliasing __float128 if the platform is not i386 or AMD64. Other platforms will fall back to double precision.

Benefits:
Build will succeed on aarch64.

Possible Drawbacks:
To keep the compiler check simple, it will exclude certain exotic architectures that do support __float128, such as PowerPC.

Related GitHub Issues:
#290

[codecov]

Codecov Report

Merging #296 (293ef09) into master (a61c85d) will not change coverage.
The diff coverage is n/a.

❗ Current head 293ef09 differs from pull request most recent head 45fef80. Consider uploading reports for the commit 45fef80 to get more accurate results

@@            Coverage Diff            @@
##            master      #296   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         1451      1458    +7     
=========================================
+ Hits          1451      1458    +7     

Impacted Files	Coverage Δ
thewalrus/__init__.py	100.00% <0.00%> (ø)
thewalrus/quantum/fock_tensors.py	100.00% <0.00%> (ø)
thewalrus/_hermite_multidimensional.py	100.00% <0.00%> (ø)

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[sduquemesa]

Hi @brownj85, thanks for your contribution! 🚀
I have created a new check so that we test if the build on aarch64 works successfully.

[nquesada]

@brownj85 @sduquemesa note that in the development version of the walrus we do not use C++ for permanents anymore. I think this PR can be closed and just wait til the next release.

[thisac]

Closing this since the dependency on C++ has been removed in the latest release.