support platform-independent feature toggles

Replace hardcoded platform checks with feature toggles to allow users to
configure gunit for their platform, e.g. if lacking POSIX features like
backtrace() and popen().

Feature Flags added:
1. GUNIT_HAS_BACKTRACE - Controls backtrace() and backtrace_symbols()
support
2. GUNIT_HAS_ADDR2LINE - Controls popen()/pclose() and addr2line
functionality
3. GUNIT_HAS_DEMANGLE - Controls C++ name demangling via cxxabi.h
4. GUNIT_HAS_PROGNAME - Controls program name retrieval

Author: thorsten-klein

include/GUnit/Detail/ProgUtils.h

@@ -7,7 +7,43 @@
 //
 #pragma once
 
-#if !defined(_WIN32) && !defined(_WIN64)
+// Feature detection: backtrace support
+#if !defined(GUNIT_HAS_BACKTRACE)
+  #if (defined(__APPLE__) || defined(__linux__)) && !defined(__ZEPHYR__)
+    #define GUNIT_HAS_BACKTRACE 1
+  #else
+    #define GUNIT_HAS_BACKTRACE 0
+  #endif
+#endif
+
+// Feature detection: addr2line support (requires popen/pclose)
+#if !defined(GUNIT_HAS_ADDR2LINE)
+  #if (defined(__APPLE__) || defined(__linux__)) && !defined(__ZEPHYR__)
+    #define GUNIT_HAS_ADDR2LINE 1
+  #else
+    #define GUNIT_HAS_ADDR2LINE 0
+  #endif
+#endif
+
+// Feature detection: C++ name demangling
+#if !defined(GUNIT_HAS_DEMANGLE)
+  #if !defined(_WIN32) && !defined(_WIN64) && !defined(__ZEPHYR__)
+    #define GUNIT_HAS_DEMANGLE 1
+  #else
+    #define GUNIT_HAS_DEMANGLE 0
+  #endif
+#endif
+
+// Feature detection: program name
+#if !defined(GUNIT_HAS_PROGNAME)
+  #if (defined(__APPLE__) || defined(__linux__)) && !defined(__ZEPHYR__)
+    #define GUNIT_HAS_PROGNAME 1
+  #else
+    #define GUNIT_HAS_PROGNAME 0
+  #endif
+#endif
+
+#if GUNIT_HAS_DEMANGLE
 #include <cxxabi.h>
 #endif
 
@@ -16,13 +52,13 @@
 
 #include "gtest/gtest.h"
 
-#if defined(__APPLE__) || defined(__linux__)
+#if GUNIT_HAS_BACKTRACE
 #include <execinfo.h>
 #endif
 
 #if defined(__APPLE__)
 #include <libproc.h>
-#elif defined(__linux__)
+#elif GUNIT_HAS_PROGNAME && defined(__linux__)
 extern const char *__progname_full;
 #elif defined(_WIN32)
 static const char *__progname_full = "progname_not_availabe_on_WIN32";
@@ -37,43 +73,42 @@ inline namespace v1 {
 namespace detail {
 
 inline std::string demangle(const std::string &mangled) {
-#if !defined(_WIN32) && !defined(_WIN64)
+#if GUNIT_HAS_DEMANGLE
   const auto demangled = abi::__cxa_demangle(mangled.c_str(), 0, 0, 0);
   if (demangled) {
     std::shared_ptr<char> free{demangled, std::free};
     return demangled;
   }
+  return {};
 #else
   return mangled;
 #endif
-  return {};
 }
 
 inline auto &progname() {
-#if defined(__linux__)
-  static auto self = __progname_full;
-#elif defined(__APPLE__)
-  static char self[PROC_PIDPATHINFO_MAXSIZE] = {};
-  proc_pidpath(getpid(), self, sizeof(self));
+#if GUNIT_HAS_PROGNAME
+  #if defined(__APPLE__)
+    static char self[PROC_PIDPATHINFO_MAXSIZE] = {};
+    proc_pidpath(getpid(), self, sizeof(self));
+  #elif defined(__linux__)
+    static auto self = __progname_full;
+  #endif
 #elif defined(_WIN32)
   static auto self = __progname_full;
+#else
+  static const char *self = "embedded_target";
 #endif
   return self;
 }
 
 inline std::string call_stack(const std::string &newline, int stack_begin = 1,
                               int stack_size = GUNIT_SHOW_STACK_SIZE) {
-#if defined(_WIN32)
-  (void)newline;
-  (void)stack_begin;
-  (void)stack_size;
-  return "callstack not availabe on WIN32";
-#else
+#if GUNIT_HAS_BACKTRACE
   static constexpr auto MAX_CALL_STACK_SIZE = 64;
   void *bt[MAX_CALL_STACK_SIZE];
   const auto frames = backtrace(bt, sizeof(bt) / sizeof(bt[0]));
   const auto symbols = backtrace_symbols(bt, frames);
-  std::shared_ptr<char *> free{symbols, std::free};
+  std::shared_ptr<char*> free{symbols, [](char** p) { std::free(p); }};
   std::stringstream result;
   stack_size += stack_begin;
 
@@ -100,14 +135,16 @@ inline std::string call_stack(const std::string &newline, int stack_begin = 1,
     }
   }
   return result.str();
+#else
+  (void)newline;
+  (void)stack_begin;
+  (void)stack_size;
+  return "callstack disabled or not available";
 #endif
 }
 
 inline std::pair<std::string, int> addr2line(void *addr) {
-#if defined(_WIN32)
-  (void)addr;
-  return {"addr2line not availabe on WIN32", 0};
-#else
+#if GUNIT_HAS_ADDR2LINE
   std::stringstream cmd;
   cmd << "addr2line -Cpe " << progname() << " " << addr;
 
@@ -128,6 +165,9 @@ inline std::pair<std::string, int> addr2line(void *addr) {
   std::string res2 = data.substr(0, space);
   const auto colon = res2.find(":");
   return {res2.substr(0, colon), std::atoi(res2.substr(colon + 1).c_str())};
+#else
+  std::ignore = addr;
+  return {"addr2line disabled or not available", 0};
 #endif
 }