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.

---
Changes since v1:

- Use both libssl and libcrypto when calling pkg-config, because some symbols of libcrypto are used directly by u-boot. This wasn't visible with static linking because -lssl -lcrypto are returned by pkg-config, but was visible with dynamic linking since only -lssl was returned by pkg-config.

 tools/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 4bbb153..8ff9c2e 100644
@@ -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)

2.1.0

Applied to u-boot/master, thanks!

Tom
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