[flang] Fix issue#202 by avoiding clang+BSD/Darwin header bug

Original-commit: flang-compiler/f18@1bdefe528a
Reviewed-on: https://github.com/flang-compiler/f18/pull/209
Tree-same-pre-rewrite: false

flang/lib/evaluate/integer.h

@@ -33,6 +33,10 @@
 #include <string>
 #include <type_traits>
 
+// Some environments, viz. clang on Darwin, allow the macro HUGE
+// to leak out of <math.h> even when it is never directly included.
+#undef HUGE
+
 namespace Fortran::evaluate::value {
 
 // Implements an integer as an assembly of smaller host integer parts

flang/lib/evaluate/real.h

@@ -22,6 +22,10 @@
 #include <limits>
 #include <string>
 
+// Some environments, viz. clang on Darwin, allow the macro HUGE
+// to leak out of <math.h> even when it is never directly included.
+#undef HUGE
+
 namespace Fortran::evaluate::value {
 
 // Models IEEE binary floating-point numbers (IEEE 754-2008,