Bug 1513798 - Automatically set -syslibroot for OSX cross-builds from configure. r=nalexander

Differential Revision: https://phabricator.services.mozilla.com/D14384

build/macosx/cross-mozconfig.common

@@ -24,7 +24,6 @@ CROSS_PRIVATE_FRAMEWORKS=$CROSS_SYSROOT/System/Library/PrivateFrameworks
 export CC="$topsrcdir/clang/bin/clang"
 export CXX="$topsrcdir/clang/bin/clang++"
 export LLVMCONFIG=$topsrcdir/clang/bin/llvm-config
-export LDFLAGS="-Wl,-syslibroot,$CROSS_SYSROOT"
 export BINDGEN_CFLAGS="-isysroot $CROSS_SYSROOT"
 export DSYMUTIL=$topsrcdir/build/macosx/llvm-dsymutil
 mk_add_options "export REAL_DSYMUTIL=$topsrcdir/llvm-dsymutil/bin/dsymutil"

build/moz.configure/toolchain.configure

@@ -1892,7 +1892,21 @@ def select_linker(linker, c_compiler, developer_options, enable_gold,
 
 
 set_config('LINKER_KIND', select_linker.KIND)
-add_old_configure_assignment('LINKER_LDFLAGS', select_linker.LINKER_FLAG)
+
+
+@depends_if(select_linker, macos_sdk)
+def linker_ldflags(linker, macos_sdk):
+    flags = list(linker.LINKER_FLAG or [])
+    if macos_sdk:
+        if linker.KIND == 'ld64':
+            flags.append('-Wl,-syslibroot,%s' % macos_sdk)
+        else:
+            flags.append('-Wl,--sysroot=%s' % macos_sdk)
+
+    return flags
+
+
+add_old_configure_assignment('LINKER_LDFLAGS', linker_ldflags)
 
 
 # There's a wrinkle with MinGW: linker configuration is not enabled, so