Breakage on Julia v1.0

https://github.com/JuliaMath/IntegerMathUtils.jl/pull/3/files#diff-28602f93a5d315a5d6dfd2d013de41a6b0bcbd3ed01c7ca21dca919edc4b78fbR13 seems to have broken this package on Julia v1.0, since the macro `@ccall` is not defined. Perhaps the support for v1.0 should be dropped if it isn't supported.

Start with the referenced pull request diff and locate the use of the undefined @ccall macro. Reproduce the package failure on Julia v1.0, then determine whether compatibility can be restored or whether the project should explicitly drop Julia v1.0 support. Done means the compatibility decision is implemented and verified against the affected package behavior.

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