Explicitly check for cygwin make when building on win32.

Bug #288303 r=bsmedberg

client.mk

@@ -193,6 +193,16 @@ LOCALES_CO_TAG       =
 
 BUILD_MODULES = all
 
+#######################################################################
+# Check for cygwin make on win32
+#
+UNAME := $(shell uname -s)
+ifneq (,$(filter CYGWIN% WIN%,$(UNAME)))
+_IS_CYGWIN_MAKE := $(findstring built for i686-pc-cygwin,$(shell $(MAKE) -h))
+ifeq (,$(_IS_CYGWIN_MAKE))
+$(error Cygwin make is required to build Mozilla. If you typed 'gmake', try 'make' instead)
+endif
+endif
 
 #######################################################################
 # Defines

configure.in

@@ -521,9 +521,13 @@ esac
 
 dnl Be sure the make we use is GNU make.
 dnl on win32, gmake.exe is the generally the wrong version
-case "$target_os" in
+case "$host_os" in
 cygwin*|mingw*|mks*|msvc*)
     AC_PATH_PROGS(MAKE, $MAKE make gmake, :)
+    _cygwin_make=`$MAKE -h | grep 'built for i686-pc-cygwin' 2>/dev/null`
+    if test -z "$_cygwin_make"; then
+        AC_MSG_ERROR([Cygwin make must be used to build Mozilla on win32.])
+    fi
     ;;
 *)
     AC_PATH_PROGS(MAKE, $MAKE gmake make, :)