[XEN PATCH v2] build: Replace `which` with `command -v`

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

The `which` command is not standard, may not exist on the build host,
or may not behave as expected by the build system. It is recommended
to use `command -v` to find out if a command exist and have its path,
and it's part of a POSIX shell standard (at least, it seems to be
mandatory since IEEE Std 1003.1-2008, but was optional before).

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Tested-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---

Notes:
    v2:
    - also replace it in xen/build.mk
    - mention that it's a mandatory feature since edition 2008.
    - some other rework of the commit message.

 xen/Makefile | 4 ++--
 xen/build.mk | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/Makefile b/xen/Makefile
index 21832d6402..767e47d6c7 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -25,8 +25,8 @@ export XEN_BUILD_HOST := $(shell hostname)
 endif
 
 # Best effort attempt to find a python interpreter, defaulting to Python 3 if
-# available.  Fall back to just `python` if `which` is nowhere to be found.
-PYTHON_INTERPRETER     := $(word 1,$(shell which python3 python python2 
2>/dev/null) python)
+# available.  Fall back to just `python`.
+PYTHON_INTERPRETER     := $(word 1,$(shell command -v python3 || command -v 
python || command -v python2) python)
 export PYTHON          ?= $(PYTHON_INTERPRETER)
 
 export CHECKPOLICY     ?= checkpolicy
diff --git a/xen/build.mk b/xen/build.mk
index 26dd5a8e87..0f490ca71b 100644
--- a/xen/build.mk
+++ b/xen/build.mk
@@ -1,6 +1,6 @@
 quiet_cmd_banner = BANNER  $@
 define cmd_banner
-    if which figlet >/dev/null 2>&1 ; then \
+    if command -v figlet >/dev/null 2>&1 ; then \
        echo " Xen $(XEN_FULLVERSION)" | figlet -f $< > $@.tmp; \
     else \
        echo " Xen $(XEN_FULLVERSION)" > $@.tmp; \
-- 
Anthony PERARD