Fix EventPipe source using COMPILE_OPTIONS on old CMake 3.6.2. (#48809)

Older CMake < 3.11 doesn't include COMPILE_OPTIONS source file property.
This property is needed by clang or it will issue warning when building
files with .c extension under c++ compiler.

Fallback to add_compile_options if CMake is older than 3.11. Even if
that option has wider scope, this is only applied to files in eventpipe
directory or in debug-pal.

Keeping the more precise set_source_files_properties on newer CMake and
when we can upgrade CMake to 3.11 or newer we could get rid of this.

src/coreclr/debug/debug-pal/CMakeLists.txt

@@ -38,7 +38,11 @@ if(CLR_CMAKE_HOST_UNIX)
 
     set (EVENTPIPE_PAL_SOURCES "${SHARED_EVENTPIPE_DIR}/ds-ipc-posix.c")
     set_source_files_properties(${EVENTPIPE_PAL_SOURCES} PROPERTIES LANGUAGE CXX)
-    set_source_files_properties(${EVENTPIPE_PAL_SOURCES} PROPERTIES COMPILE_OPTIONS -xc++)
+    if (CMAKE_VERSION VERSION_GREATER 3.11 OR CMAKE_VERSION VERSION_EQUAL 3.11)
+        set_source_files_properties(${EVENTPIPE_PAL_SOURCES} PROPERTIES COMPILE_OPTIONS -xc++)
+    else(CMAKE_VERSION VERSION_GREATER 3.11 OR CMAKE_VERSION VERSION_EQUAL 3.11)
+        add_compile_options(-xc++)
+    endif()
 
     set(TWO_WAY_PIPE_SOURCES
       ${EVENTPIPE_PAL_SOURCES}

src/coreclr/vm/eventing/eventpipe/CMakeLists.txt

@@ -65,7 +65,11 @@ set_source_files_properties(${SHARED_EVENTPIPE_SOURCE_PATH}/ds-sources.c PROPERT
 set_source_files_properties(${EVENTPIPE_SOURCES} PROPERTIES LANGUAGE CXX)
 
 if(CLR_CMAKE_HOST_UNIX)
-  set_source_files_properties(${EVENTPIPE_SOURCES} PROPERTIES COMPILE_OPTIONS -xc++)
+  if (CMAKE_VERSION VERSION_GREATER 3.11 OR CMAKE_VERSION VERSION_EQUAL 3.11)
+    set_source_files_properties(${EVENTPIPE_SOURCES} PROPERTIES COMPILE_OPTIONS -xc++)
+  else(CMAKE_VERSION VERSION_GREATER 3.11 OR CMAKE_VERSION VERSION_EQUAL 3.11)
+    add_compile_options(-xc++)
+  endif()
 endif(CLR_CMAKE_HOST_UNIX)
 
 list(APPEND CORECLR_EVENTPIPE_SHIM_SOURCES