use autoconf' macros for this

configure.ac

@@ -209,27 +209,16 @@ then
 	)
 fi
 
-WIN=0
-AC_MSG_CHECKING([whether CC compiles for Windows API])
+CFLAGS="$cstd -Wno-pedantic-ms-format -Werror"
+AC_MSG_CHECKING([whether CC supports and needs -Wno-pedantic-ms-format])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#ifndef _WIN32
 #error wants windows
 #endif]], [])],
 	[AC_MSG_RESULT([yes])]
-	[WIN=1],
+	[cstd="$cstd -Wno-pedantic-ms-format"],
 	[AC_MSG_RESULT([no])]
 )
 
-if test "$WIN" -eq 1
-then
-	CFLAGS="$cstd -Wno-pedantic-ms-format -Werror"
-	AC_MSG_CHECKING([whether CC supports and needs -Wno-pedantic-ms-format])
-	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
-		[AC_MSG_RESULT([yes])]
-		[cstd="$cstd -Wno-pedantic-ms-format"],
-		[AC_MSG_RESULT([no])]
-	)
-fi
-
 if test "x$ed25519impl" = "xdonna"
 then
 	CFLAGS="$cstd -Wno-unused-function -Werror"
@@ -320,12 +309,6 @@ yes|pcre2)
 	;;
 esac
 
-EXESFX=''
-if test "$WIN" -eq 1
-then
-	EXESFX='.exe'
-fi
-
 # recreate dir tree, because otherwise gcc will fuck up
 (cd "$srcdir" && find ed25519 -type d) | xargs mkdir -p
 
@@ -335,5 +318,4 @@ AC_SUBST(MYDEFS,["$MYDEFS"])
 AC_SUBST(MAINLIB,["$MAINLIB"])
 AC_SUBST(NOPIE,["$nopie"])
 AC_SUBST(SRCDIR,["$srcdir"])
-AC_SUBST(EXESFX,["$EXESFX"])
 AC_OUTPUT(Makefile)