tools: use pkg-config when available to get SSL flags

Instead of hardcoding -lssl -lcrypto as the flags needed to build
mkimage with FIT signature enabled, use pkg-config when
available. This allows to properly support cases where static linking
is used, which requires linking with -lz, since OpenSSL uses zlib
internally.

We gracefully fallback on the previous behavior of hardcoding -lssl
-lcrypto if pkg-config is not available or fails with an error.
Signed-off-by: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>

tools/Makefile

@@ -122,7 +122,8 @@ endif
 
 # MXSImage needs LibSSL
 ifneq ($(CONFIG_MX23)$(CONFIG_MX28)$(CONFIG_FIT_SIGNATURE),)
-HOSTLOADLIBES_mkimage += -lssl -lcrypto
+HOSTLOADLIBES_mkimage += \
+	$(shell pkg-config --libs libssl libcrypto 2> /dev/null || echo "-lssl -lcrypto")
 endif
 
 HOSTLOADLIBES_dumpimage := $(HOSTLOADLIBES_mkimage)