this should really fix the XCode 6/7 builds

test/CMakeLists.txt

@@ -61,13 +61,9 @@ add_library(doctest_main OBJECT
     "src/unit.cpp"
 )
 set_target_properties(doctest_main PROPERTIES
+    COMPILE_DEFINITIONS "$<$<CXX_COMPILER_ID:MSVC>:_SCL_SECURE_NO_WARNINGS>"
     COMPILE_OPTIONS "$<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>"
 )
-target_compile_definitions(doctest_main PUBLIC
-    "$<$<CXX_COMPILER_ID:MSVC>:_SCL_SECURE_NO_WARNINGS>"
-    "DOCTEST_THREAD_LOCAL"
-    "DOCTEST_CONFIG_SUPER_FAST_ASSERTS"
-)
 target_compile_features(doctest_main PUBLIC cxx_std_11)
 target_include_directories(doctest_main PRIVATE "thirdparty/doctest")
 
@@ -100,6 +96,9 @@ foreach(file ${files})
     string(REGEX REPLACE "unit-([^$]+)" "test-\\1" testcase ${file_basename})
 
     add_executable(${testcase} $<TARGET_OBJECTS:doctest_main> ${file})
+    target_compile_definitions(${testcase} PRIVATE
+      DOCTEST_CONFIG_SUPER_FAST_ASSERTS
+    )
     target_compile_options(${testcase} PRIVATE
         $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
         $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>

test/thirdparty/doctest/doctest_compatibility.h

 #ifndef DOCTEST_COMPATIBILITY
 #define DOCTEST_COMPATIBILITY
 
+#define DOCTEST_THREAD_LOCAL // enable single-threaded builds on XCode 6/7 - https://github.com/onqtam/doctest/issues/172
 #include "doctest.h"
 
 // Catch doesn't require a semicolon after CAPTURE but doctest does