Fix Build for Android.

[jlsantiago0]

Some versions of CMake set CMAKE_SYSTEM_NAME to "Android" check CMAKE_SYSTEM_NAME case insensitively for that string.

Also with the new atomic functions being used by the SRT library, we need to link the atomic library for Android targets.

[maxsharabayko]

@jlsantiago0 Thank you for the fix!
There is one more way to perform a case-insensitive comparison. But it would require an additional variable to be set.

string(TOLOWER ${CMAKE_BUILD_TYPE} LOWERCASE_CMAKE_BUILD_TYPE)
set_if(ANDROID ${LOWERCASE_CMAKE_BUILD_TYPE} MATCHES "android")

Therefore your solution looks cleaner to me.