[build] Fix pc file generation when use mbedtls

mbedtls doesn't create .pc file by itself. Put mbedtls under
Requires.private leads to pkg-config check error.

CMakeLists.txt

@@ -283,14 +283,29 @@ if (ENABLE_ENCRYPTION)
 		link_directories(
 			${SSL_LIBRARY_DIRS}
 		)
-	else() # Common for mbedtls and openssl
-		if ("${USE_ENCLIB}" STREQUAL "mbedtls")
-			add_definitions(-DUSE_MBEDTLS=1)
-			set (SSL_REQUIRED_MODULES "mbedtls mbedcrypto")
-		else()
-			add_definitions(-DUSE_OPENSSL=1)
-			set (SSL_REQUIRED_MODULES "openssl libcrypto")
+	elseif ("${USE_ENCLIB}" STREQUAL "mbedtls")
+		add_definitions(-DUSE_MBEDTLS=1)
+		if ("${SSL_LIBRARY_DIRS}" STREQUAL "")
+			set(MBEDTLS_PREFIX "${CMAKE_PREFIX_PATH}" CACHE PATH "The path of mbedtls")
+			find_package(MbedTLS REQUIRED)
+			set (SSL_INCLUDE_DIRS ${MBEDTLS_INCLUDE_DIR})
+			set (SSL_LIBRARIES  ${MBEDTLS_LIBRARIES})
+		endif()
+		if ("${SSL_LIBRARIES}" STREQUAL "")
+			set (SSL_LIBRARIES  mbedtls mbedcrypto)
 		endif()
+		message(STATUS "SSL enforced mbedtls: -I ${SSL_INCLUDE_DIRS} -l;${SSL_LIBRARIES}")
+
+		foreach(LIB ${SSL_LIBRARIES})
+			if(IS_ABSOLUTE ${LIB} AND EXISTS ${LIB})
+				set (SRT_LIBS_PRIVATE ${SRT_LIBS_PRIVATE} ${LIB})
+			else()
+				set(SRT_LIBS_PRIVATE ${SRT_LIBS_PRIVATE} "-l${LIB}")
+			endif()
+		endforeach()
+	else() # openssl
+		add_definitions(-DUSE_OPENSSL=1)
+		set (SSL_REQUIRED_MODULES "openssl libcrypto")
 		# Try using pkg-config method first if enabled,
 		# fall back to find_package method otherwise
 		if (USE_OPENSSL_PC)
@@ -315,24 +330,12 @@ if (ENABLE_ENCRYPTION)
 			)
 			message(STATUS "SSL via pkg-config: -L ${SSL_LIBRARY_DIRS} -I ${SSL_INCLUDE_DIRS} -l;${SSL_LIBRARIES}")
 		else()
-			if ("${USE_ENCLIB}" STREQUAL "mbedtls")
-				if ("${SSL_LIBRARY_DIRS}" STREQUAL "")
-					set(MBEDTLS_PREFIX "${CMAKE_PREFIX_PATH}" CACHE PATH "The path of mbedtls")
-					find_package(MbedTLS REQUIRED)
-					set (SSL_INCLUDE_DIRS ${MBEDTLS_INCLUDE_DIR})
-					set (SSL_LIBRARIES  ${MBEDTLS_LIBRARIES})
-				endif()
-				if ("${SSL_LIBRARIES}" STREQUAL "")
-					set (SSL_LIBRARIES  mbedtls mbedcrypto)
-				endif()
-				message(STATUS "SSL enforced mbedtls: -I ${SSL_INCLUDE_DIRS} -l;${SSL_LIBRARIES}")
-			else()
-				find_package(OpenSSL REQUIRED)
-				set (SSL_INCLUDE_DIRS ${OPENSSL_INCLUDE_DIR})
-				set (SSL_LIBRARIES ${OPENSSL_LIBRARIES})
-				message(STATUS "SSL via find_package(OpenSSL): -I ${SSL_INCLUDE_DIRS} -l;${SSL_LIBRARIES}")
-			endif()
+			find_package(OpenSSL REQUIRED)
+			set (SSL_INCLUDE_DIRS ${OPENSSL_INCLUDE_DIR})
+			set (SSL_LIBRARIES ${OPENSSL_LIBRARIES})
+			message(STATUS "SSL via find_package(OpenSSL): -I ${SSL_INCLUDE_DIRS} -l;${SSL_LIBRARIES}")
 		endif()
+
 	endif()
 
 	add_definitions(-DSRT_ENABLE_ENCRYPTION)