package/qemu: filter out long make options

Since qemu started using ninja, they have the following fragment in the
Makefile:

MAKE.n = $(findstring n,$(firstword $(MAKEFLAGS)))
NINJAFLAGS = ... $(if $(MAKE.n), -n) ...

Buildroot's generated makefile in the O= directory invokes make in the
base buildroot with --no-print-directory. However, make's placement of
the --no-print-directory in MAKEFLAGS varies between the versions of
the host make; make 4.3 places that at the end while make 3.82 places
it at the beginning. As a result, if building on a system with an older
host make, qemu's makefile invokes `ninja -n` which does not generate
any outputs.

To reproduce, on a CentOS 7 machine or docker image:
  mkdir /tmp/br-build && cd /tmp/br-build
  make -C ~/buildroot pc_x86_64_bios_defconfig O=`pwd`
  make menuconfig # Switch to glibc, enable "QEMU" and "QEMU tools"
  make all # Build succeeds
  find target -name qemu-img # No binary has been built

Pick up the fix commited in Qemu upstream.

Signed-off-by: Alexey Neyman <stilor@att.net>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/qemu/0004-Makefile-ignore-long-options.patch

@@ -0,0 +1,41 @@
+From 14833e24dea49303ebc2464813601054b6cdfcac Mon Sep 17 00:00:00 2001
+From: Alexey Neyman <stilor@att.net>
+Date: Wed, 21 Jul 2021 19:08:46 -0700
+Subject: [PATCH] Makefile: ignore long options
+
+When searching for options like -n in MAKEFLAGS, current code may result
+in a false positive match when make is invoked with long options like
+--no-print-directory. This has been observed with certain versions of
+host make (e.g. 3.82) while building the Qemu package in buildroot.
+
+Filter out such long options before searching for one-character options.
+
+Signed-off-by: Alexey Neyman <stilor@att.net>
+Message-Id: <20210722020846.3678817-1-stilor@att.net>
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+---
+ Makefile | 8 +++++---
+ 1 file changed, 5 insertions(+), 3 deletions(-)
+
+diff --git a/Makefile b/Makefile
+index 6c36330eef..401c623a65 100644
+--- a/Makefile
++++ b/Makefile
+@@ -129,9 +129,11 @@ endif
+ # 4. Rules to bridge to other makefiles
+ 
+ ifneq ($(NINJA),)
+-MAKE.n = $(findstring n,$(firstword $(MAKEFLAGS)))
+-MAKE.k = $(findstring k,$(firstword $(MAKEFLAGS)))
+-MAKE.q = $(findstring q,$(firstword $(MAKEFLAGS)))
++# Filter out long options to avoid flags like --no-print-directory which
++# may result in false positive match for MAKE.n
++MAKE.n = $(findstring n,$(firstword $(filter-out --%,$(MAKEFLAGS))))
++MAKE.k = $(findstring k,$(firstword $(filter-out --%,$(MAKEFLAGS))))
++MAKE.q = $(findstring q,$(firstword $(filter-out --%,$(MAKEFLAGS))))
+ MAKE.nq = $(if $(word 2, $(MAKE.n) $(MAKE.q)),nq)
+ NINJAFLAGS = $(if $V,-v) $(if $(MAKE.n), -n) $(if $(MAKE.k), -k0) \
+         $(filter-out -j, $(lastword -j1 $(filter -l% -j%, $(MAKEFLAGS)))) \
+-- 
+2.27.0
+