Fix debug build for windows

msvcc.sh

@@ -42,7 +42,7 @@
 # format and translated into something sensible for cl or ml.
 #
 
-args="-nologo"
+args="-nologo -W3"
 md=-MD
 cl="cl"
 ml="ml"
@@ -67,13 +67,25 @@ do
       safeseh=
       shift 1
     ;;
+    -O0)
+      args="$args -Od"
+      shift 1
+    ;;
     -O*)
-      args="$args $1"
+      # If we're optimizing, make sure we explicitly turn on some optimizations
+      # that are implicitly disabled by debug symbols (-Zi).
+      args="$args $1 -OPT:REF -OPT:ICF -INCREMENTAL:NO"
       shift 1
     ;;
     -g)
-      # Can't specify -RTC1 or -Zi in opt. -Gy is ok. Use -OPT:REF?
-      args="$args -D_DEBUG -RTC1 -Zi"
+      # Enable debug symbol generation.
+      args="$args -Zi -DEBUG"
+      shift 1
+    ;;
+    -DFFI_DEBUG)
+      # Link against debug CRT and enable runtime error checks.
+      args="$args -RTC1"
+      defines="$defines $1"
       md=-MDd
       shift 1
     ;;
@@ -110,8 +122,8 @@ do
       shift 1
     ;;
     -Wall)
-      # -Wall on MSVC is overzealous. Use -W3 instead.
-      args="$args -W3"
+      # -Wall on MSVC is overzealous, and we already build with -W3. Nothing
+      # to do here.
       shift 1
     ;;
     -Werror)