simplify hardening check logic, disable for mingw

Rather than doing separate linker/compiler checks, just build a
non-empty program with each so that the compiler will actually try to
use the hardening features. Reduce redundancy in the macro calls by just
setting the flag that was just tested.

Also, disable hardening for mingw, since its trying to use a
libssp-0.dll file that I can't find right now. The detected hardening
flags break mingw builds currently.

configure.ac

@@ -80,58 +80,53 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [[
 AC_MSG_RESULT([$CLANG])
 AS_IF([test "x$CLANG" == "xyes"], [CLANG_FLAGS=-Qunused-arguments])
 
-# We want to check for compiler flag support. Prior to clang v5.1, there was no way to make
-# clang's "argument unused" warning fatal.  So we invoke the compiler through a
-# wrapper script that greps for this message.
+# We want to check for compiler flag support. Prior to clang v5.1, there was no
+# way to make clang's "argument unused" warning fatal.  So we invoke the
+# compiler through a wrapper script that greps for this message.
 saved_CC="$CC"
 saved_LD="$LD"
 flag_wrap="$srcdir/scripts/wrap-compiler-for-flag-check"
 CC="$flag_wrap $CC"
 LD="$flag_wrap $LD"
 
-AC_DEFUN([check_cflag],
-	[AX_CHECK_COMPILE_FLAG([$1], [$2], [$3], [-Werror $4])])
-AC_DEFUN([check_ldflag],
-	[AX_CHECK_LINK_FLAG([$1], [$2], [$3], [-Werror $4])])
-
-
 AC_ARG_ENABLE([hardening],
-	[AS_HELP_STRING([--disable-hardening], [Disable options to frustrate memory corruption exploits])],
-	[],
-	[enable_hardening=yes])
-
-HARDEN_CFLAGS=""
-HARDEN_LDFLAGS=""
-AS_IF([test "x$enable_hardening" == "xyes"], [
+	[AS_HELP_STRING([--disable-hardening],
+			[Disable options to frustrate memory corruption exploits])],
+	[], [enable_hardening=yes])
+
+AC_DEFUN([CHECK_CFLAG],
+	 [AC_LANG_ASSERT(C)
+	  AC_MSG_CHECKING([if $saved_CC supports "$1"])
+	  old_cflags="$CFLAGS"
+	  CFLAGS=[$1]
+	  AC_TRY_LINK([#include <stdio.h>],
+		      [printf("Hello")],
+		      AC_MSG_RESULT([yes])
+		      HARDEN_CFLAGS="$HARDEN_CFLAGS [$1]",
+		      AC_MSG_RESULT([no])
+		      $2
+		      )
+	  ])
+
+AS_IF([test "x$enable_hardening" == "xyes" -a "x$HOST_OS" != "xwin"], [
 	# Tell GCC to NOT optimize based on signed arithmetic overflow
-	check_cflag([-fno-strict-overflow], [HARDEN_CFLAGS="$HARDEN_CFLAGS -fno-strict-overflow"])
+	CHECK_CFLAG([-fno-strict-overflow])
 
 	# _FORTIFY_SOURCE replaces builtin functions with safer versions.
-	check_cflag([-D_FORTIFY_SOURCE=2], 
-		[HARDEN_CFLAGS="$HARDEN_CFLAGS -D_FORTIFY_SOURCE=2"])
-
-	# Use stack-protector-strong if available; if not, fallback to stack-protector-all which
-	# is considered to be overkill
-	check_cflag([-fstack-protector-strong], 
-		[STACK_PROTECT="-fstack-protector-strong"],
-		check_cflag([-fstack-protector-all],
-			[STACK_PROTECT="-fstack-protector-all"],
-			[AC_MSG_ERROR([compiler does not support stack protection - use --disable-hardening to override if you understand the risks])]
+	CHECK_CFLAG([-D_FORTIFY_SOURCE=2])
+
+	# Use stack-protector-strong if available; if not, fallback to
+	# stack-protector-all which is considered to be overkill
+	CHECK_CFLAG([-fstack-protector-strong],
+		CHECK_CFLAG([-fstack-protector-all],
+			AC_MSG_ERROR([compiler does appear to support stack protection
+			  - use --disable-hardening to override])
 		)
 	)
 
-	check_ldflag([$STACK_PROTECT],
-		[HARDEN_CFLAGS="$HARDEN_CFLAGS $STACK_PROTECT"
-		 check_cflag([-Wstack-protector], [HARDEN_CFLAGS="$HARDEN_CFLAGS -Wstack-protector"],
-		 	[], [$STACK_PROTECT])
-		],
-		[AC_MSG_ERROR([compiler supports stack protection but linker does not])]
-	)
-
 	# Enable read only relocations
-	check_ldflag([-Wl,-z,relro],
-   		[HARDEN_LDFLAGS="$HARDEN_LDFLAGS -Wl,-z,relro"
-    	check_ldflag([-Wl,-z,now], [HARDEN_LDFLAGS="$HARDEN_LDFLAGS -Wl,-z,now"])])
+	CHECK_CFLAG([-Wl,-z,relro])
+	CHECK_CFLAG([-Wl,-z,now])
 ])
 
 # Restore CC, LD