mhz: respect CC and CFLAGS passed by buildsystem

It seems that the Makefile has both CC and CFLAGS hardcoded and does not
allow overriding them by ones being passed by the buildsystem.

This works fine until CONFIG_PKG_ASLR_PIE_ALL is selected, then building
will fail with:
arm-openwrt-linux-muslgnueabi/bin/ld.bfd: mhz.o: relocation R_ARM_MOVW_ABS_NC against `a local symbol' can not be used when making a shared object; recompile with -fPIC
arm-openwrt-linux-muslgnueabi/bin/ld.bfd: mhz.o(.text+0x75c): unresolvable R_ARM_CALL relocation against symbol `__aeabi_l2d@@GCC_3.5

So, lets add a patch pending upstream that allows both CC and CFLAGS to be
overriden so that ones passed by the buildsystem are actually respected.

Fixes: 89123b308f ("mhz: add new package")
Signed-off-by: Robert Marko <robimarko@gmail.com>

utils/mhz/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mhz
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=https://github.com/wtarreau/mhz.git

utils/mhz/patches/0001-Makefile-allow-overriding-CC-and-CFLAGS.patch

@@ -0,0 +1,29 @@
+From d55f7b578eb2126d2e4a7f045321f6ba7df3800a Mon Sep 17 00:00:00 2001
+From: Robert Marko <robimarko@gmail.com>
+Date: Wed, 30 Aug 2023 20:31:07 +0200
+Subject: [PATCH] Makefile: allow overriding CC and CFLAGS
+
+For OpenWrt and Buildroot which support really large amount of different
+architectures and cores it is sometimes required to pass our own CFLAGS.
+This is especially true if hardening options are to be respected.
+
+Also, for cross-compiling CC should be respected as currently it is
+working since both OpenWrt and Buildroot symlink gcc to the cross compiler.
+
+So, lets set the current values as defaults but allow them to be overriden.
+
+Signed-off-by: Robert Marko <robimarko@gmail.com>
+---
+ Makefile | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/Makefile
++++ b/Makefile
+@@ -1,5 +1,5 @@
+-CC         := gcc
+-CFLAGS     := -O3 -Wall -fomit-frame-pointer
++CC         ?= gcc
++CFLAGS     ?= -O3 -Wall -fomit-frame-pointer
+ 
+ all: mhz
+