Work around Ruby on MacOS Xcode 9.4 misconfiguration defining 'isfinite'
to deprecated 'finite'. Example warning:
li_std_list_wrap.cxx:7197:9: error: 'finite' is deprecated: first deprecated in macOS 10.9 [-Werror,-Wdeprecated-declarations]
if (SWIG_Float_Overflow_Check(v)) {
^
li_std_list_wrap.cxx:7156:73: note: expanded from macro 'SWIG_Float_Overflow_Check'
^
li_std_list_wrap.cxx:7122:29: note: expanded from macro 'SWIG_isfinite'
^
/Users/travis/.rvm/rubies/ruby-2.4.3/include/ruby-2.4.0/ruby/missing.h:180:24: note: expanded from macro 'isfinite'
^
/usr/include/math.h:757:12: note: 'finite' has been explicitly marked deprecated here
extern int finite(double) __OSX_AVAILABLE_BUT_DEPRECATED(__MAC_10_0, __MAC_10_9, __IPHONE_NA, __IPHONE_NA);
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