Only request per_object_debug_info when fission is enabled.

This allows CROSSTOOL authors to add flags to all targets for which fission
is enabled, even when a compile action does not output split debug info.

For example, when building with ThinLTO, compiles are split into a frontend
compile, that does not generate split debug info, but still needs to include
debug info if fission is enabled (even in opt mode).

RELNOTES: None.
PiperOrigin-RevId: 163825563

src/main/java/com/google/devtools/build/lib/rules/cpp/CcCommon.java

@@ -94,7 +94,6 @@ public void collectMetadataArtifacts(Iterable<Artifact> objectFiles,
           CppRuleClasses.HEADER_MODULE_COMPILE,
           CppRuleClasses.INCLUDE_PATHS,
           CppRuleClasses.PIC,
-          CppRuleClasses.PER_OBJECT_DEBUG_INFO,
           CppRuleClasses.PREPROCESSOR_DEFINES);
   public static final String CC_TOOLCHAIN_DEFAULT_ATTRIBUTE_NAME = ":cc_toolchain";
 

src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java

@@ -1937,6 +1937,9 @@ public ImmutableSet<String> configurationEnabledFeatures(RuleContext ruleContext
         requestedFeatures.add(CppRuleClasses.GCC_COVERAGE_MAP_FORMAT);
       }
     }
+    if (useFission()) {
+      requestedFeatures.add(CppRuleClasses.PER_OBJECT_DEBUG_INFO);
+    }
     return requestedFeatures.build();
   }