[openwrt/openwrt] build: fix `which` detection on Fedora & MacOS

[LEDE Commits]

aparcar pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/913403b587451abaaf67e8f9640f0dc2cdcec95d

commit 913403b587451abaaf67e8f9640f0dc2cdcec95d
Author: Paul Spooren <mail at aparcar.org>
AuthorDate: Fri Oct 1 15:56:27 2021 -1000

    build: fix `which` detection on Fedora & MacOS
    
    Fix Fedora 34/35 issue where 'which' detection of 'which' wasn't working
    because Fedora use alias and proc
    
    Fixup of fca5ad55d2 prereq-build: fix `which` detection on Fedora
    
    Reported-by: Jani Partanen <rtfm at iki.fi>
    Suggest-by: Etienne Champetier <champetier.etienne at gmail.com>
    Tested-by: Georgi Valkov <gvalkov at abv.bg>
    Signed-off-by: Paul Spooren <mail at aparcar.org>
    (cherry picked from commit 0d1ebf0d6d20f0439ab45b293f9daa7662c44ba6)
---
 include/prereq-build.mk | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/prereq-build.mk b/include/prereq-build.mk
index 538aee58fe..623881c93f 100644
--- a/include/prereq-build.mk
+++ b/include/prereq-build.mk
@@ -182,7 +182,9 @@ $(eval $(call SetupHostCommand,rsync,Please install 'rsync', \
 	rsync --version </dev/null))
 
 $(eval $(call SetupHostCommand,which,Please install 'which', \
-	which which | grep which))
+	/usr/bin/which which, \
+	/bin/which which, \
+	which which))
 
 $(STAGING_DIR_HOST)/bin/mkhash: $(SCRIPT_DIR)/mkhash.c
 	mkdir -p $(dir $@)