Fix XCODE_ATTRIBUTE_..._LOCATION target property lookup

Refactoring in commit v3.5.0-rc1~272^2~16 (cmGeneratorTarget: Add API for
property keys, 2015-10-25) changed the Xcode generator implementation of
`XCODE_ATTRIBUTE_...` properties to use the target `GetProperty` method on each
`XCODE_ATTRIBUTE_...` property listed by `GetPropertyKeys` instead of looping
over the property entries directly.  This made the lookup of property names of
the form `XCODE_ATTRIBUTE_..._LOCATION` accidentally trigger the computed
property logic for the undocumented/legacy `<CONFIG>_LOCATION` property.  Of
course the computed property value is not the same as the value stored in the
`XCODE_ATTRIBUTE_..._LOCATION` property.  Fix the computed property logic to
avoid triggering on `XCODE_ATTRIBUTE_...` attributes.

Closes: #16319

Source/cmTarget.cxx

@@ -1164,7 +1164,8 @@ const char* cmTarget::GetProperty(const std::string& prop,
       }
     }
     // Support "<CONFIG>_LOCATION".
-    else if (cmHasLiteralSuffix(prop, "_LOCATION")) {
+    else if (cmHasLiteralSuffix(prop, "_LOCATION") &&
+             !cmHasLiteralPrefix(prop, "XCODE_ATTRIBUTE_")) {
       std::string configName(prop.c_str(), prop.size() - 9);
       if (configName != "IMPORTED") {
         if (!this->HandleLocationPropertyPolicy(context)) {

Tests/RunCMake/XcodeProject/RunCMakeTest.cmake

@@ -1,6 +1,7 @@
 include(RunCMake)
 
 run_cmake(XcodeFileType)
+run_cmake(XcodeAttributeLocation)
 run_cmake(XcodeAttributeGenex)
 run_cmake(XcodeAttributeGenexError)
 run_cmake(XcodeObjectNeedsEscape)

Tests/RunCMake/XcodeProject/XcodeAttributeLocation-check.cmake

@@ -0,0 +1,7 @@
+set(expect "DEPLOYMENT_LOCATION = YES")
+file(STRINGS ${RunCMake_TEST_BINARY_DIR}/XcodeAttributeLocation.xcodeproj/project.pbxproj actual
+  REGEX "DEPLOYMENT_LOCATION = .*;" LIMIT_COUNT 1)
+if(NOT "${actual}" MATCHES "${expect}")
+  message(SEND_ERROR "The actual project contains the line:\n ${actual}\n"
+    "which does not match expected regex:\n ${expect}\n")
+endif()

Tests/RunCMake/XcodeProject/XcodeAttributeLocation.cmake

@@ -0,0 +1,3 @@
+enable_language(C)
+add_executable(some main.c)
+set_property(TARGET some PROPERTY XCODE_ATTRIBUTE_DEPLOYMENT_LOCATION YES)