Add CheckSymbolExists module for FindMbedTLS.cmake

FindMbedTLS.cmake uses `check_symbol_exists` macro which requires
`include(CheckSymbolExists)` before invocation (see
https://cmake.org/cmake/help/latest/module/CheckSymbolExists.html).

Signed-off-by: Azamat H. Hackimov <[email protected]>

cmake/Modules/FindMbedTLS.cmake

@@ -94,6 +94,7 @@ if(MBEDTLS_LIB
    AND NOT MBEDX509_LIB)
   set(CMAKE_REQUIRED_LIBRARIES ${MBEDTLS_LIB})
   set(CMAKE_REQUIRED_INCLUDES ${MBEDTLS_INCLUDE_DIR})
+  include(CheckSymbolExists)
   check_symbol_exists(mbedtls_x509_crt_init "mbedtls/x509_crt.h" MBEDTLS_INCLUDES_X509)
   check_symbol_exists(mbedtls_sha256_init "mbedtls/sha256.h" MBEDTLS_INCLUDES_CRYPTO)
   unset(CMAKE_REQUIRED_INCLUDES)