--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -510,16 +510,36 @@ def host_variables(host):
     if host.kernel == 'kFreeBSD':
         os_arch = 'GNU_kFreeBSD'
     else:
         os_arch = host.kernel
     add_old_configure_assignment('HOST_OS_ARCH', os_arch)
     set_config('HOST_OS_ARCH', os_arch)
 
 
+@depends(target)
+def target_platform_defines(target):
+    if target.kernel == 'WINNT':
+        set_define('_WINDOWS', '1')
+        set_define('WIN32', '1')
+        set_define('XP_WIN', '1')
+        set_define('XP_WIN32', '1')
+    else:
+        set_define('XP_UNIX', '1')
+
+    if target.kernel == 'Darwin':
+        set_define('XP_DARWIN', '1')
+        if target.os == 'iOS':
+            set_define('XP_IOS', '1')
+        elif target.os == 'OSX':
+            set_define('XP_MACOSX', '1')
+    elif target.kernel == 'Linux':
+        set_define('XP_LINUX', '1')
+
+
 # The application/project to build
 # ==============================================================
 option('--enable-application', nargs=1, env='MOZ_BUILD_APP',
        help='Application to build. Same as --enable-project.')
 
 @depends('--enable-application', '--help')
 def application(app, help):
     if app:

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -922,17 +922,16 @@ esac
 MOZ_DOING_LTO(lto_is_enabled)
 
 dnl ========================================================
 dnl System overrides of the defaults for target
 dnl ========================================================
 
 case "$target" in
 *-darwin*)
-    AC_DEFINE(XP_DARWIN)
     MKSHLIB='$(CXX) $(CXXFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MOZ_OPTIMIZE_FLAGS="-O3 -fno-stack-protector"
     CFLAGS="$CFLAGS -fno-common"
     CXXFLAGS="$CXXFLAGS -fno-common"
     DLL_SUFFIX=".dylib"
     DSO_LDOPTS=''
     STRIP="$STRIP -x -S"
@@ -1189,20 +1188,16 @@ case "$target" in
         dnl XXX: should be -LTCG:PGOPTIMIZE, but that fails on libxul.
         dnl Probably also a compiler bug, but what can you do?
         PROFILE_USE_LDFLAGS="-LTCG:PGUPDATE"
         LDFLAGS="$LDFLAGS -DYNAMICBASE"
         RCFLAGS="-nologo"
     fi
     AC_DEFINE(HAVE_SNPRINTF)
     AC_DEFINE(HAVE__MSIZE)
-    AC_DEFINE(_WINDOWS)
-    AC_DEFINE(WIN32)
-    AC_DEFINE(XP_WIN)
-    AC_DEFINE(XP_WIN32)
     AC_DEFINE(HW_THREADS)
     AC_DEFINE(STDC_HEADERS)
     AC_DEFINE(WIN32_LEAN_AND_MEAN)
     BIN_SUFFIX='.exe'
     MOZ_USER_DIR="Mozilla"
 
     case "$host_os" in
     cygwin*|msvc*|mks*)
@@ -2772,28 +2767,16 @@ AC_SUBST(MOZ_LINKER)
 AC_SUBST(WIN32_CONSOLE_EXE_LDFLAGS)
 AC_SUBST(WIN32_GUI_EXE_LDFLAGS)
 
 AC_CHECK_FUNCS(posix_fadvise posix_fallocate)
 
 dnl Set various defines and substitutions
 dnl ========================================================
 
-if test "$OS_ARCH" = "Darwin"; then
-  if test -n "$MOZ_IOS"; then
-    AC_DEFINE(XP_IOS)
-  else
-    AC_DEFINE(XP_MACOSX)
-  fi
-  AC_DEFINE(XP_DARWIN)
-  AC_DEFINE(XP_UNIX)
-elif test "$OS_ARCH" != "WINNT"; then
-  AC_DEFINE(XP_UNIX)
-fi
-
 if test "$MOZ_DEBUG"; then
     AC_DEFINE(MOZ_REFLOW_PERF)
     AC_DEFINE(MOZ_REFLOW_PERF_DSP)
 fi
 
 dnl ========================================================
 dnl Determine options to use for running the preprocessor.
 dnl ========================================================

--- a/old-configure.in
+++ b/old-configure.in
@@ -1326,22 +1326,18 @@ case "$target" in
 #endif],
                                    [],
                                    ac_cv_ios_target="yes",
                                    ac_cv_ios_target="no")])
     if test "$ac_cv_ios_target" = "yes" -a -z $MOZ_IOS; then
        AC_MSG_ERROR([targeting iOS but not using an iOS SDK?])
     fi
     if test -n "$MOZ_IOS"; then
-        AC_DEFINE(XP_IOS)
-        AC_DEFINE(XP_DARWIN)
         direct_nspr_config=1
     else
-        AC_DEFINE(XP_MACOSX)
-        AC_DEFINE(XP_DARWIN)
         # The ExceptionHandling framework is needed for Objective-C exception
         # logging code in nsObjCExceptions.h. Currently we only use that in debug
         # builds.
         MOZ_DEBUG_LDFLAGS="$MOZ_DEBUG_LDFLAGS -framework ExceptionHandling";
     fi
 
     if test "x$lto_is_enabled" = "xyes"; then
         echo "Skipping -dead_strip because lto is enabled."
@@ -1638,20 +1634,16 @@ case "$target" in
         dnl both SSSE3 and SSE4.1.
         HAVE_TOOLCHAIN_SUPPORT_MSSSE3=1
         HAVE_TOOLCHAIN_SUPPORT_MSSE4_1=1
         dnl allow AVX2 code from VS2012
         HAVE_X86_AVX2=1
         MOZ_MEMORY=1
     fi
     AC_DEFINE(HAVE_SNPRINTF)
-    AC_DEFINE(_WINDOWS)
-    AC_DEFINE(WIN32)
-    AC_DEFINE(XP_WIN)
-    AC_DEFINE(XP_WIN32)
     AC_DEFINE(HW_THREADS)
     AC_DEFINE(STDC_HEADERS)
     AC_DEFINE(WIN32_LEAN_AND_MEAN)
     dnl See http://support.microsoft.com/kb/143208 to use STL
     AC_DEFINE(NOMINMAX)
     BIN_SUFFIX='.exe'
     MOZ_USER_DIR="Mozilla"
 
@@ -1734,23 +1726,16 @@ case "$target" in
     ;;
 
 esac
 
 AC_SUBST_LIST(MMX_FLAGS)
 AC_SUBST_LIST(SSE_FLAGS)
 AC_SUBST_LIST(SSE2_FLAGS)
 
-case "$target" in
-*-*linux*)
-    # Includes linux-android
-    AC_DEFINE(XP_LINUX)
-    ;;
-esac
-
 AC_SUBST(MOZ_LINKER)
 if test -n "$MOZ_LINKER"; then
   AC_DEFINE(MOZ_LINKER)
 fi
 
 dnl Only one oddball right now (QNX), but this gives us flexibility
 dnl if any other platforms need to override this in the future.
 AC_DEFINE_UNQUOTED(D_INO,$DIRENT_INO)
@@ -7719,20 +7704,16 @@ if test "$MOZ_X11"; then
 
 fi # MOZ_X11
 
 fi # COMPILE_ENVIRONMENT
 
 dnl Set various defines and substitutions
 dnl ========================================================
 
-if test "$OS_ARCH" != "WINNT"; then
-  AC_DEFINE(XP_UNIX)
-fi
-
 if test "$MOZ_DEBUG"; then
     AC_DEFINE(MOZ_REFLOW_PERF)
     AC_DEFINE(MOZ_REFLOW_PERF_DSP)
 fi
 
 if test "$ACCESSIBILITY" -a "$MOZ_ENABLE_GTK" ; then
     AC_DEFINE(MOZ_ACCESSIBILITY_ATK)
     ATK_FULL_VERSION=`$PKG_CONFIG --modversion atk`