Grackle update

Fix a few issues with grackle. Now requires the latest version of grackle.

added 1 commit

• 97c07f67 - Update grackle doc

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added 1 commit

• cdf7f1f3 - Remove useless fortran flag

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assigned to @matthieu

added 2 commits

• 046af37e - Check for grackle library before adding wraning flags to the compiler command line.
• 65d64099 - Code formatting

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merged

mentioned in commit fb210c79