Add configure option --with-macos-deployment-target

aclocal.m4

@@ -1091,6 +1091,35 @@ AC_DEFUN([CHECK_GMP],
 AC_REQUIRE([AC_PROG_CC])
 ])
 
+# FP_MACOS_DEPLOYMENT_TARGET
+# --------------------------
+AC_DEFUN([FP_MACOS_DEPLOYMENT_TARGET],
+[
+if test "x$TargetOS_CPP-$TargetVendor_CPP" = "xdarwin-apple"; then
+  AC_MSG_CHECKING([Mac OS X deployment target])
+  case $MACOS_DEPLOYMENT_TARGET in
+    none)  ;;
+    10.4)  MACOS_DEPLOYMENT_VERSION=10.4
+    	   MACOS_DEPLOYMENT_SDK=/Developer/SDKs/MacOSX10.4u.sdk
+	   ;;
+    10.4u) MACOS_DEPLOYMENT_VERSION=10.4
+    	   MACOS_DEPLOYMENT_SDK=/Developer/SDKs/MacOSX10.4u.sdk
+	   ;;
+    *)     MACOS_DEPLOYMENT_VERSION=$MACOS_DEPLOYMENT_TARGET
+    	   MACOS_DEPLOYMENT_SDK=/Developer/SDKs/MacOSX${MACOS_DEPLOYMENT_TARGET}.sdk
+	   ;;
+  esac
+  if test "x$MACOS_DEPLOYMENT_TARGET" = "xnone"; then
+    AC_MSG_RESULT(none)
+  else
+    if test ! -d $MACOS_DEPLOYMENT_SDK; then
+      AC_MSG_ERROR([Unknown deployment target $MACOS_DEPLOYMENT_TARGET])
+    fi
+    AC_MSG_RESULT([${MACOS_DEPLOYMENT_VERSION} (${MACOS_DEPLOYMENT_SDK})])
+  fi
+fi
+])
+
 # --------------------------------------------------------------
 # Calculate absolute path to build tree
 # --------------------------------------------------------------

configure.ac

@@ -819,6 +819,23 @@ AC_ARG_ENABLE(dotnet,
 )
 AC_SUBST(DotnetSupport)
 
+dnl ** Mac OS X: explicit deployment target
+dnl --------------------------------------------------------------
+AC_ARG_WITH([macos-deployment-target],
+[AC_HELP_STRING([--macos-deployment-target=VERSION],
+        [Build for Mac OS VERSION and higher  [default= version of build host]])],
+[MACOS_DEPLOYMENT_TARGET="$withval"
+ if test "x$TargetOS_CPP-$TargetVendor_CPP" != "xdarwin-apple"; then
+   # ignore everywhere, but on Mac OS
+   AC_MSG_WARN([--macos-deployment-target is only available on Mac OS X])
+   MACOS_DEPLOYMENT_TARGET=none
+ fi],
+[MACOS_DEPLOYMENT_TARGET=none]
+)
+FP_MACOS_DEPLOYMENT_TARGET
+AC_SUBST(MACOS_DEPLOYMENT_VERSION)
+AC_SUBST(MACOS_DEPLOYMENT_SDK)
+
 dnl --------------------------------------------------------------
 dnl End of configure script option section
 dnl --------------------------------------------------------------

mk/config.mk.in

@@ -185,6 +185,11 @@ BootingFromUnregisterisedHc = @BootingFromUnregisterisedHc@
 #
 XMLDocWays=
 
+# Mac OS X deployment target (to cross-compile for older OS versions)
+#
+MACOS_DEPLOYMENT_VERSION = @MACOS_DEPLOYMENT_VERSION@
+MACOS_DEPLOYMENT_SDK = @MACOS_DEPLOYMENT_SDK@
+
 ################################################################################
 #
 # Variables that control how the compiler itself is built