xtensa: support for C++ library using Xtensa toolchain

Changes needed to build C++ code using Xtensa toolchain.

Signed-off-by: William Tambe <williamt@cadence.com>

Author: williamtcdns

cmake/compiler/xt-clang/compiler_flags.cmake

@@ -11,7 +11,7 @@ set_compiler_property(PROPERTY nostdinc_include)
 # For C++ code, re-add the standard includes directory which was
 # cleared up from nostdinc_inlcude in above lines with no
 # "include-fixed" this time"
-if(CONFIG_CPP)
+if(CONFIG_CPP AND NOT CONFIG_XTENSA_LIBC)
   execute_process(
     COMMAND ${CMAKE_C_COMPILER} --print-file-name=include/stddef.h
     OUTPUT_VARIABLE _OUTPUT

cmake/linker/xt-ld/linker_flags.cmake

@@ -8,7 +8,11 @@ check_set_linker_property(TARGET linker PROPERTY base
 )
 
 if(NOT CONFIG_NATIVE_LIBRARY AND NOT CONFIG_EXTERNAL_MODULE_LIBCPP)
-  set_property(TARGET linker PROPERTY cpp_base -lstdc++)
+  if (CONFIG_XTENSA_LIBC)
+    set_property(TARGET linker PROPERTY cpp_base -lstdc++11)
+  else()
+    set_property(TARGET linker PROPERTY cpp_base -lstdc++)
+  endif()
 endif()
 
 check_set_linker_property(TARGET linker PROPERTY baremetal