Add yaml-cpp to the shared libraries if building with system yaml-cpp

[spinnau]

Fixes #668

Changes proposed in this pull request:

• If building Cantera with system_yamlcpp=y the yaml-cpp library needs to be specified in the linker flags.

[codecov]

Codecov Report

Merging #671 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #671      +/-   ##
==========================================
+ Coverage   70.78%   70.78%   +<.01%     
==========================================
  Files         373      373              
  Lines       43454    43454              
==========================================
+ Hits        30757    30758       +1     
+ Misses      12697    12696       -1

Impacted Files	Coverage Δ
src/transport/GasTransport.cpp	90.58% <0%> (+0.2%)	⬆️

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[codecov]

Codecov Report

Merging #671 into master will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #671      +/-   ##
==========================================
+ Coverage   70.66%   70.78%   +0.11%     
==========================================
  Files         372      373       +1     
  Lines       43507    43454      -53     
==========================================
+ Hits        30745    30758      +13     
+ Misses      12762    12696      -66

Impacted Files	Coverage Δ
test_problems/pureFluidTest/testPureWater.cpp	96.87% <0%> (-0.1%)	⬇️
include/cantera/zeroD/ReactorFactory.h	100% <0%> (ø)	⬆️
include/cantera/zeroD/WallFactory.h	64.28% <0%> (ø)	⬆️
include/cantera/zeroD/FlowDeviceFactory.h	64.28% <0%> (ø)	⬆️
include/cantera/zeroD/Wall.h	50% <0%> (ø)	⬆️
include/cantera/PureFluid.h	66.66% <0%> (ø)
test_problems/rankine_democxx/rankine.cpp	93.87% <0%> (+0.39%)	⬆️
src/clib/ctreactor.cpp	7.77% <0%> (+0.76%)	⬆️
src/kinetics/importKinetics.cpp	98.4% <0%> (+0.8%)	⬆️
src/clib/Cabinet.h	33.96% <0%> (+7.54%)	⬆️
... and 10 more

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[bryanwweber]

I pushed a few more changes to fix the compiling issue I was having on macOS with system_yamlcpp and remove linking to libfmt, since we use the header-only version now to my understanding.

@speth Can you take a look and verify that these changes are correct?

[spinnau]

@bryanwweber: Compiles and works fine for me on Linux with your changes and system_fmt=y.