Fix 'make dist' on powerpc64 by include an atomic.S place holder file.

Add EXTRA_DIST atomic.c for powerpc64 to ensure source is packaged.

lib/libspl/asm-powerpc64/Makefile.am

@@ -2,11 +2,14 @@ include $(top_srcdir)/config/Rules.am
 
 DEFAULT_INCLUDES += \
         -I${top_srcdir}/lib/libspl/include
-COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) \
-	  $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS)
+
 atomic_SOURCE = atomic.c
 atomic_ASM = atomic.S
 
+COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) \
+	  $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS)
+EXTRA_DIST = ${atomic_SOURCE}
+
 # Generates assembly to simplify inclusion in ../Makefile.am
 all-am:
 	$(COMPILE) -c -S ${atomic_SOURCE} -o ${atomic_ASM}

lib/libspl/asm-powerpc64/atomic.S

@@ -0,0 +1,6 @@
+Stub file for 'make dist' distdir rule.
+
+This file is directly referenced by ../Makefile.am as a source
+file and thus will be expected by 'make dist'.  To avoid this
+being a problem this stub file was added.  It will be overwritten
+at build time based on assmebly generated from atomic.c.