[openwrt/openwrt] Makefile: fix stray \ warnings with grep-3.8

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/af88bdb1700cae8a789f8a3ea52499f35c29af6f

commit af88bdb1700cae8a789f8a3ea52499f35c29af6f
Author: Nick Hainke <vincent at systemli.org>
AuthorDate: Sun Sep 11 08:15:52 2022 +0200

    Makefile: fix stray \ warnings with grep-3.8
    
    We simply grep for "/usr". So no need for "-E" or "\/". Furthermore, in
    the new grep versions this creates warnings.
    
    As written in the grep-3.8 announcement:
      Regular expressions with stray backslashes now cause warnings, as
      their unspecified behavior can lead to unexpected results.
      For example, '\a' and 'a' are not always equivalent
      <https://bugs.gnu.org/39678>.
    
    Fixes warnings in the form of:
      grep: warning: stray \ before /
    
    Signed-off-by: Nick Hainke <vincent at systemli.org>
    (cherry picked from commit a29d3bc48c40c6a2a93ae1806bea2ac26455cdbb)
    [ fix conflict error ]
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index e18bc18608..11531d4760 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ $(if $(findstring $(space),$(TOPDIR)),$(error ERROR: The path to the OpenWrt dir
 
 world:
 
-DISTRO_PKG_CONFIG:=$(shell which -a pkg-config | grep -E '\/usr' | head -n 1)
+DISTRO_PKG_CONFIG:=$(shell which -a pkg-config | grep '/usr' | head -n 1)
 export PATH:=$(TOPDIR)/staging_dir/host/bin:$(PATH)
 
 ifneq ($(OPENWRT_BUILD),1)