Platform (OpenBSD): uses getexecpath(3) if available

Fixes https://github.com/fastfetch-cli/fastfetch/issues/2195#issuecomment-6095513342

CMakeLists.txt

@@ -1689,6 +1689,13 @@ if(FreeBSD OR OpenBSD OR NetBSD)
     unset(CMAKE_REQUIRED_DEFINITIONS)
 endif()
 
+if(OpenBSD)
+    check_symbol_exists("getexecpath" "unistd.h" HAVE_GETEXECPATH)
+    if(HAVE_GETEXECPATH)
+        target_compile_definitions(libfastfetch PUBLIC FF_HAVE_GETEXECPATH=1)
+    endif()
+endif()
+
 if(HAVE_PIPE2)
     target_compile_definitions(libfastfetch PUBLIC FF_HAVE_PIPE2)
 endif()

src/common/impl/FFPlatform_unix.c

@@ -64,7 +64,11 @@ static void getExePath(FFPlatform* platform) {
         exePathLen--; // remove terminating NUL
     }
 #elif defined(__OpenBSD__)
-    // OpenBSD doesn't have a reliable way to get the executable path.
+#if FF_HAVE_GETEXECPATH
+    // https://man.openbsd.org/getexecpath.3
+    size_t exePathLen = getexecpath(exePath, sizeof(exePath)) == 0 ? strlen(exePath) : 0;
+#else
+    // OpenBSD (before 8.0) doesn't have a reliable way to get the executable path.
     // Current implementation uses argv[0], which can be easily spoofed.
     // See #2195
     size_t exePathLen = 0;
@@ -165,6 +169,7 @@ static void getExePath(FFPlatform* platform) {
             }
         }
     }
+#endif
 #elif defined(__sun)
     ssize_t exePathLen = readlink("/proc/self/path/a.out", exePath, sizeof(exePath) - 1);
     if (exePathLen > 0) {