x86/vdso: Fix flip/flop vdso build bug

Two consecutive "make" on an already compiled kernel tree will show
different behavior:

$ make
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CHK     include/generated/compile.h
  VDSOCHK arch/x86/entry/vdso/vdso64.so.dbg
  VDSOCHK arch/x86/entry/vdso/vdso32.so.dbg
Kernel: arch/x86/boot/bzImage is ready  (#3)
  Building modules, stage 2.
  MODPOST 12 modules

$ make
make
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CHK     include/generated/compile.h
  VDSO    arch/x86/entry/vdso/vdso64.so.dbg
  OBJCOPY arch/x86/entry/vdso/vdso64.so
  VDSO2C  arch/x86/entry/vdso/vdso-image-64.c
  CC      arch/x86/entry/vdso/vdso-image-64.o
  VDSO    arch/x86/entry/vdso/vdso32.so.dbg
  OBJCOPY arch/x86/entry/vdso/vdso32.so
  VDSO2C  arch/x86/entry/vdso/vdso-image-32.c
  CC      arch/x86/entry/vdso/vdso-image-32.o
  AR      arch/x86/entry/vdso/built-in.a
  AR      arch/x86/entry/built-in.a
  AR      arch/x86/built-in.a
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o
<snip>

This is causing "LD vmlinux" once every two times even without any
modifications. This is the same bug fixed in commit 92a47286
("x86/boot: Fix if_changed build flip/flop bug"). Two "if_changed" cannot
be used in one target.

Fix this merging two commands into one function.

Fixes: 7ac87074 ("x86/vdso: Switch to generic vDSO implementation")
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://lkml.kernel.org/r/20190712101556.17833-1-naohiro.aota@wdc.com

arch/x86/entry/vdso/Makefile

@@ -56,8 +56,7 @@ VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \
 			-z max-page-size=4096
 
 $(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE
-	$(call if_changed,vdso)
-	$(call if_changed,vdso_check)
+	$(call if_changed,vdso_and_check)
 
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include -I$(srctree)/include/uapi -I$(srctree)/arch/$(SUBARCH)/include/uapi
 hostprogs-y			+= vdso2c
@@ -127,8 +126,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
 $(obj)/vdsox32.so.dbg: $(obj)/vdsox32.lds $(vobjx32s) FORCE
-	$(call if_changed,vdso)
-	$(call if_changed,vdso_check)
+	$(call if_changed,vdso_and_check)
 
 CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
 VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -soname linux-gate.so.1
@@ -167,8 +165,7 @@ $(obj)/vdso32.so.dbg: FORCE \
 		      $(obj)/vdso32/note.o \
 		      $(obj)/vdso32/system_call.o \
 		      $(obj)/vdso32/sigreturn.o
-	$(call if_changed,vdso)
-	$(call if_changed,vdso_check)
+	$(call if_changed,vdso_and_check)
 
 #
 # The DSO images are built using a special linker script.
@@ -184,6 +181,9 @@ VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
 	-Bsymbolic
 GCOV_PROFILE := n
 
+quiet_cmd_vdso_and_check = VDSO    $@
+      cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
+
 #
 # Install the unstripped copies of vdso*.so.  If our toolchain supports
 # build-id, install .build-id links as well.