[CMake] [macho_embedded] Only set sys root if the variable is set, this prevents passing empty -isysroot arguments

This is a minor cleanup to the macho_embedded builtins.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@252619 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/cmake/Modules/CompilerRTDarwinUtils.cmake b/cmake/Modules/CompilerRTDarwinUtils.cmake
index 1719506..0edee65 100644
--- a/cmake/Modules/CompilerRTDarwinUtils.cmake
+++ b/cmake/Modules/CompilerRTDarwinUtils.cmake
@@ -161,8 +161,11 @@
     ${ARGN})
   set(libname "${name}.${suffix}_${LIB_ARCH}_${LIB_OS}")
   add_library(${libname} STATIC ${LIB_SOURCES})
+  if(DARWIN_${LIB_OS}_SYSROOT)
+    set(sysroot_flag -isysroot ${DARWIN_${LIB_OS}_SYSROOT})
+  endif()
   set_target_compile_flags(${libname}
-    -isysroot ${DARWIN_${LIB_OS}_SYSROOT}
+    ${sysroot_flag}
     ${DARWIN_${LIB_OS}_BUILTIN_MIN_VER_FLAG}
     ${LIB_CFLAGS})
   set_property(TARGET ${libname} APPEND PROPERTY
@@ -409,6 +412,7 @@
         set(float_flag)
         if(${arch} MATCHES "^arm")
           set(DARWIN_macho_embedded_SYSROOT ${DARWIN_ios_SYSROOT})
+          set(DARWIN_macho_embedded_BUILTIN_MIN_VER_FLAG ${DARWIN_ios_BUILTIN_MIN_VER_FLAG})
           # x86 targets are hard float by default, but the complain about the
           # float ABI flag, so don't pass it unless we're targeting arm.
           set(float_flag ${${float_type}_FLOAT_FLAG})