feature switch for thread local variables and multi-threading

thread local variables will trigger a memory allocation on a bare metal system.
use a macro to define the variable as thread local. Bare metal by definition has no
threads and so needs no qualifier.

CMakeLists.txt

@@ -19,6 +19,7 @@ set(SNITCH_MAX_PATH_LENGTH          1024 CACHE STRING "Maximum length of a file
 # Feature toggles.
 set(SNITCH_DEFINE_MAIN                     ON  CACHE BOOL "Define main() in snitch -- disable to provide your own main() function.")
 set(SNITCH_WITH_EXCEPTIONS                 ON  CACHE BOOL "Use exceptions in snitch implementation -- will be forced OFF if exceptions are not available.")
+set(SNITCH_WITH_MULTITHREADING             ON  CACHE BOOL "Multi-threading support and thread local variables -- disable if needed.")
 set(SNITCH_WITH_TIMINGS                    ON  CACHE BOOL "Measure the time taken by each test case -- disable to speed up tests.")
 set(SNITCH_WITH_SHORTHAND_MACROS           ON  CACHE BOOL "Use short names for test macros -- disable if this causes conflicts.")
 set(SNITCH_CONSTEXPR_FLOAT_USE_BITCAST     ON  CACHE BOOL "Use std::bit_cast if available to implement exact constexpr float-to-string conversion.")

include/snitch/snitch_config.hpp.config

@@ -77,6 +77,9 @@
 #if !defined(SNITCH_WITH_CATCH2_REPORTER)
 #cmakedefine01 SNITCH_WITH_CATCH2_REPORTER
 #endif
+#if !defined(SNITCH_WITH_MULTITHREADING)
+#cmakedefine01 SNITCH_WITH_MULTITHREADING
+#endif
 #if !defined(SNITCH_SHARED_LIBRARY)
 #cmakedefine01 SNITCH_SHARED_LIBRARY
 #endif
@@ -97,6 +100,12 @@
 #    define SNITCH_WITH_EXCEPTIONS 0
 #endif
 
+#if defined(SNITCH_WITH_MULTITHREADING)
+#    define SNITCH_THREAD_LOCAL thread_local
+#else
+#    define SNITCH_THREAD_LOCAL
+#endif
+
 #if !defined(__cpp_lib_bit_cast)
 #    undef SNITCH_CONSTEXPR_FLOAT_USE_BITCAST
 #    define SNITCH_CONSTEXPR_FLOAT_USE_BITCAST 0

meson_options.txt

@@ -15,6 +15,7 @@ option('max_path_length'          ,type: 'integer' ,value: 1024, description: 'M
 # Feature toggles.
 option('define_main'                     ,type: 'boolean' ,value: true, description: 'Define main() in snitch -- disable to provide your own main() function.')
 option('with_exceptions'                 ,type: 'boolean' ,value: true, description: 'Use exceptions in snitch implementation -- will be forced OFF if exceptions are not available.')
+option('with_multithreading'             ,type: 'boolean', value: true, description: 'Multi-threading support and thread local variables -- disable if needed.')
 option('with_timings'                    ,type: 'boolean' ,value: true, description: 'Measure the time taken by each test case -- disable to speed up tests.')
 option('with_shorthand_macros'           ,type: 'boolean' ,value: true, description: 'Use short names for test macros -- disable if this causes conflicts.')
 option('constexpr_float_use_bitcast'     ,type: 'boolean' ,value: true, description: 'Use std::bit_cast if available to implement exact constexpr float-to-string conversion.')

src/snitch_test_data.cpp

@@ -6,7 +6,7 @@
 
 namespace snitch::impl {
 namespace {
-thread_local test_state* thread_current_test = nullptr;
+SNITCH_THREAD_LOCAL test_state* thread_current_test = nullptr;
 }
 
 test_state& get_current_test() noexcept {