package/Makefile.in: set GIT_DIR=. in {HOST, TARGET}_MAKE_ENV

A number of packages try to detect if they are running in a git repo and run
git describe at build time instead of using the hard coded version number if
it succeed, leading to odd version numbers as they end up picking up the
Buildroot git version if building inside a Buildroot git checkout, E.G.:

rauc --version
rauc 2023.11-562-g9c954953b4+

This is because rauc builds with meson and uses vcs_tag:

https://github.com/rauc/rauc/blob/v1.11/meson.build#L168-L171

https://mesonbuild.com/Reference-manual_functions.html#vcs_tag

Another example is micropython, where we already work around it by passing
GIT_DIR=.

In the context of Buildroot the packages are never built in their own git
checkout, so pass GIT_DIR=.  to ensure git doesn't walk back up the
directory tree and finds the Buildroot git repo, which fixes the rauc (and
similar) issues.

>>> rauc 1.11 Building
..
ninja: Entering directory `/home/peko/source/buildroot/output-rauc/build/rauc-1.11//build'
[1/29] Generating version.h with a custom command
fatal: not a git repository: '.'

cat output-rauc/build/rauc-1.11/build/version.h
 #define PACKAGE_STRING "rauc 1.11"

 #define PACKAGE_VERSION "1.11"

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit c07aafa087)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/Makefile.in

@@ -263,7 +263,9 @@ export PERL=$(shell which perl)
 # finds this perl module by exporting the proper value for PERL5LIB.
 export PERL5LIB=$(HOST_DIR)/lib/perl
 
-TARGET_MAKE_ENV = PATH=$(BR_PATH)
+TARGET_MAKE_ENV = \
+	GIT_DIR=. \
+	PATH=$(BR_PATH)
 
 TARGET_CONFIGURE_OPTS = \
 	$(TARGET_MAKE_ENV) \
@@ -307,6 +309,7 @@ TARGET_CONFIGURE_OPTS = \
 
 
 HOST_MAKE_ENV = \
+	GIT_DIR=. \
 	PATH=$(BR_PATH) \
 	PKG_CONFIG="$(PKG_CONFIG_HOST_BINARY)" \
 	PKG_CONFIG_SYSROOT_DIR="/" \