tools: fix annoying "mkdir -p ..." logs when building tools in parallel

When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
show awkward "mkdir -p ..." logs.

  $ make -j16
    [ snip ]
  mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
  mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids

Defining MAKEFLAGS=<value> on the command line wipes out command line
switches from the resultant MAKEFLAGS definition, even though the command
line switches are active. [1]

MAKEFLAGS puts all single-letter options into the first word, and that
word will be empty if no single-letter options were given. [2]
However, this breaks if MAKEFLAGS=<value> is given on the command line.

The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
line, which breaks the following code in tools/scripts/Makefile.include:

    short-opts := $(firstword -$(MAKEFLAGS))

If MAKEFLAGS really needs modification, it should be done through the
environment variable, as follows:

    MAKEFLAGS=<value> $(MAKE) ...

That said, I question whether modifying MAKEFLAGS is necessary here.
The only flag we might want to exclude is --no-print-directory, as the
tools build system changes the working directory. However, people might
find the "Entering/Leaving directory" logs annoying.

I simply removed the offending MAKEFLAGS=<value>.

[1]: https://savannah.gnu.org/bugs/?62469
[2]: https://www.gnu.org/software/make/manual/make.html#Testing-Flags

Fixes: ea01fa9 ("tools: Connect to the kernel build system")
Fixes: a50e433 ("perf tools: Honor parallel jobs")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Daniel Xu <dxu@dxuuu.xyz>

Author: masahir0y

Makefile

@@ -1421,18 +1421,13 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
 	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
 endif
 
-# Clear a bunch of variables before executing the submake
-ifeq ($(quiet),silent_)
-tools_silent=s
-endif
-
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
 
 tools/%: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
 
 # ---------------------------------------------------------------------------
 # Kernel selftest