[openwrt/openwrt] prereq-build: fix `which` detection on Fedora

[LEDE Commits]

aparcar pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/fca5ad55d292f8e481406123d0e95b3c85d39733

commit fca5ad55d292f8e481406123d0e95b3c85d39733
Author: Jani Partanen <rtfm at iki.fi>
AuthorDate: Thu Sep 30 23:51:37 2021 +0300

    prereq-build: fix `which` detection on Fedora
    
    Fix Fedora 34/35 issue where 'which' detection of 'which' wasn't working
    because Fedora use alias and proc
    
    Signed-off-by: Jani Partanen <rtfm at iki.fi>
    [fix commit subject and message]
    Signed-off-by: Paul Spooren <mail at aparcar.org>
---
 include/prereq-build.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/prereq-build.mk b/include/prereq-build.mk
index 9242407b18..750d334716 100644
--- a/include/prereq-build.mk
+++ b/include/prereq-build.mk
@@ -186,7 +186,7 @@ $(eval $(call SetupHostCommand,rsync,Please install 'rsync', \
 	rsync --version </dev/null))
 
 $(eval $(call SetupHostCommand,which,Please install 'which', \
-	which which | grep which))
+	env which which | grep which))
 
 $(STAGING_DIR_HOST)/bin/mkhash: $(SCRIPT_DIR)/mkhash.c
 	mkdir -p $(dir $@)