Only define _USE_MATH_DEFINES on Windows platforms

The _USE_MATH_DEFINES macro is only needed on Windows to expose math
constants like M_PI in math.h/cmath.

CMakeLists.txt

@@ -87,7 +87,9 @@ target_link_libraries(${module_name}
 )
 
 # Add definition _USE_MATH_DEFINES to enable math constant definitions from math.h/cmath.
-target_compile_definitions(${module_name} PRIVATE _USE_MATH_DEFINES)
+if (WIN32)
+    target_compile_definitions(${module_name} PRIVATE _USE_MATH_DEFINES)
+endif()
 
 #Set target properties
 set_property(TARGET ${module_name} PROPERTY POSITION_INDEPENDENT_CODE ON)

unit_tests/CMakeLists.txt

@@ -21,7 +21,9 @@ file(GLOB_RECURSE src_files "*.cpp")
 
 add_executable(tests${module_name} ${src_files})
 
-target_compile_definitions(tests${module_name} PRIVATE _USE_MATH_DEFINES)
+if (WIN32)
+    target_compile_definitions(tests${module_name} PRIVATE _USE_MATH_DEFINES)
+endif()
 
 target_link_libraries(tests${module_name} PRIVATE ${module_name})