[bug#39372] Chicken Scheme: Update version to 5.1.0 and add gcc-toolchain

[Ekaitz at ElenQ Technology]

Hi,

I made a patch for chicken-scheme according to this conversation in the 
help-guix mailing list:

https://lists.gnu.org/archive/html/help-guix/2020-01/msg00230.html

I pushed the version to 5.1.0 and added gcc-toolchain as a propagated-input as 
the conversation suggested. The reason is without the gcc-toolchain csc (the 
chicken compiler) is unable to deal with -lm (math library), which is not 
installed with the current chicken package.

The linked conversation suggests that gcc-toolchain is a fundamental part of 
chicken so it should be a dependency of it.

Sorry if I didn't follow the format, but I was unable to find a good 
contributing guide.

Best,

Ekaitz

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