package/mutt: fix libgpgme static build

Fix the following static build failure with libgpgme raised since at
least bump to version 2.2.9 in commit
7a2afdb7b1180bed3b6ad92c22c908805467ead3:

/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4a-buildroot-linux-musl/11.3.0/../../../../sh4a-buildroot-linux-musl/bin/ld: /home/autobuild/autobuild/instance-11/output-1/host/sh4a-buildroot-linux-musl/sysroot/usr/lib/libgpgme.a(assuan-support.o): in function `my_usleep':
assuan-support.c:(.text+0x260): undefined reference to `__assuan_usleep'

Fixes:
 - http://autobuild.buildroot.org/results/0680dbc95601fcd8cdf07b926ea5e9be2079c7bf
 - http://autobuild.buildroot.org/results/b4f2d1ad77fb8b97accc4150d8249de145cb9cf4

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit b518b0f161c81582f31c79c50552b5106f693df2)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mutt/mutt.mk

@@ -40,7 +40,11 @@ MUTT_CONF_OPTS += \
 
 # Force the path to "gpgrt-config" (from the libgpg-error package) to
 # avoid using the one on host, if present.
-MUTT_CONF_ENV += GPGRT_CONFIG=$(STAGING_DIR)/usr/bin/gpgrt-config
+MUTT_GPGRT_CONFIG = $(STAGING_DIR)/usr/bin/gpgrt-config
+ifeq ($(BR2_STATIC_LIBS),y)
+MUTT_GPGRT_CONFIG += --static
+endif
+MUTT_CONF_ENV += GPGRT_CONFIG="$(MUTT_GPGRT_CONFIG)"
 else
 MUTT_CONF_OPTS += --disable-gpgme
 endif