[libmysql] Fix issue #5046

[PhoebeHui]

libmysql installed failed on Linux, ${CMAKE_SYSTEM_PROCESSOR} didn’t get the value here, apply the patch for fix this issue.

The error message likes:
CMAKE_REQUIRED_LIBRARIES is set to:
m;crypt;dl;-lpthread;rt;atomic
For compatibility with CMake 3.11 and below this check is ignoring it.
Call Stack (most recent call first):
configure.cmake:188 (CHECK_INCLUDE_FILES)
CMakeLists.txt:653 (INCLUDE)
This warning is for project developers. Use -Wno-dev to suppress it.

CMake Error at configure.cmake:459 (STRING):
STRING no output variable specified
Call Stack (most recent call first):
CMakeLists.txt:653 (INCLUDE)

[vicroms]

Hi Phoebe,
The real issue we need to solve is why ${CMAKE_SYSTEM_PROCESSOR} is not set to the right value.
Changes must be made in the Linux toolchain so that the right value is detected and set; l will take a look at this PR during the week.

[PhoebeHui]

Thank you Victor for pointing out this!

[vicroms]

There was some previous work done to address this issue in #4688.

[JackBoosY]

@vicroms , the related PR is #4970.

[vicroms]

Superseded by #6442