Fix for building lex scanners on Windows when scanner is generated by flex 2.5.35 on Linux

src/StepFile/step.lex

@@ -40,9 +40,15 @@ void rec_typarg(int argtype);
   void resultat ()           /* Resultat alloue dynamiquement, "jete" une fois lu */
       { if (modcom == 0) rec_restext(yytext,yyleng); }
 
-// disable MSVC warnings in flex code
+// MSVC specifics
 #ifdef _MSC_VER
+
+// disable MSVC warnings in flex code
 #pragma warning(disable:4131 4244 4273 4267 4127)
+
+// Avoid includion of unistd.h if parser is generated on Linux (flex 2.5.35)
+#define YY_NO_UNISTD_H
+
 #endif
 
 // disable GCC warnings in flex code