Separate COMPILE_DEFINITIONS: preprocessor flags
and      COMPILE_FLAGS:       compiler flags
when setting source files properties.

Usually the distincion does not matter, but sometimes it does
(e.g. doing cross compilation).

cmake documentation says:
COMPILE_FLAGS: Additional flags to be added when compiling this source file.

These flags will be added to the list of compile flags when this
source file builds. Use COMPILE_DEFINITIONS to pass additional
preprocessor definitions.

Change-Id: I8bc02609be1b5c113562832109b2e948c2278bec
(cherry picked from commit 06383cb023fce6c667bae6899bcd1b47b3f983b8)