Unset FEATURE_EVENTSOURCE_XPLAT in macOS builds (#48244)

Author: sywhang

src/coreclr/clr.featuredefines.props

@@ -13,7 +13,7 @@
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(TargetsUnix)' == 'true'">
-        <FeatureXplatEventSource>true</FeatureXplatEventSource>
+        <FeatureXplatEventSource Condition="'$(TargetOS)'!='OSX'">true</FeatureXplatEventSource>
 
         <FeatureArrayStubAsIL>true</FeatureArrayStubAsIL>
         <FeatureMulticastStubAsIL>true</FeatureMulticastStubAsIL>

src/coreclr/clrdefinitions.cmake

@@ -120,9 +120,9 @@ endif(FEATURE_GDBJIT_LANGID_CS)
 if(FEATURE_GDBJIT_SYMTAB)
     add_definitions(-DFEATURE_GDBJIT_SYMTAB)
 endif(FEATURE_GDBJIT_SYMTAB)
-if(CLR_CMAKE_TARGET_UNIX)
+if(CLR_CMAKE_TARGET_LINUX)
     add_definitions(-DFEATURE_EVENTSOURCE_XPLAT)
-endif(CLR_CMAKE_TARGET_UNIX)
+endif(CLR_CMAKE_TARGET_LINUX)
 # NetBSD doesn't implement this feature
 if(NOT CLR_CMAKE_TARGET_NETBSD)
     add_definitions(-DFEATURE_HIJACK)