8315060: Out of tree incremental build fails with ccache

Reviewed-by: kbarrett, dholmes

make/autoconf/build-performance.m4

@@ -243,8 +243,11 @@ AC_DEFUN([BPERF_SETUP_CCACHE_USAGE],
       fi
     fi
 
+    # The CCACHE_BASEDIR needs to end with '/' as ccache will otherwise think
+    # directories next to it, that have the base dir name as a prefix, are sub
+    # directories of CCACHE_BASEDIR.
     CCACHE="CCACHE_COMPRESS=1 $SET_CCACHE_DIR \
-        CCACHE_SLOPPINESS=$CCACHE_SLOPPINESS CCACHE_BASEDIR=$TOPDIR $CCACHE"
+        CCACHE_SLOPPINESS=$CCACHE_SLOPPINESS CCACHE_BASEDIR=$WORKSPACE_ROOT/ $CCACHE"
 
     if test "x$SET_CCACHE_DIR" != x; then
       mkdir -p $CCACHE_DIR > /dev/null 2>&1

make/common/NativeCompilation.gmk

@@ -224,9 +224,12 @@ endif
 # object files while CCACHE_BASEDIR will make ccache relativize all paths for
 # its compiler. The compiler then produces relative dependency files.
 # make does not know a relative and absolute filename is the same so it will
-# ignore such dependencies.
+# ignore such dependencies. This only applies when the OUTPUTDIR is inside
+# the WORKSPACE_ROOT.
 ifneq ($(CCACHE), )
-  REWRITE_PATHS_RELATIVE = true
+  ifneq ($(filter $(WORKSPACE_ROOT)/%, $(OUTPUTDIR)), )
+    REWRITE_PATHS_RELATIVE = true
+  endif
 endif
 
 ifeq ($(REWRITE_PATHS_RELATIVE), true)