Fix non-ASCII characters in VPI test files to pass t_dist_whitespace

Replace the section sign and em-dash characters with ASCII equivalents
in t_flag_main_vpi.cpp and t_flag_main_vpi_lib2.cpp. The t_dist_whitespace
CI check rejects non-ASCII content in source files.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test_regress/t/t_flag_main_vpi.cpp

@@ -85,10 +85,10 @@ static void register_callbacks() {
     vpi_register_cb(&cb_data);
 }
 
-// IEEE 1800 §37: vlog_startup_routines[] — null-terminated array of startup functions
+// IEEE 1800 section 37: vlog_startup_routines[] -- null-terminated array of startup functions
 extern "C" {
 void (*vlog_startup_routines[])() = {register_callbacks, nullptr};
 
-// Named bootstrap entrypoint — used when library is loaded as <path>:my_vpi_bootstrap
+// Named bootstrap entrypoint -- used when library is loaded as <path>:my_vpi_bootstrap
 void my_vpi_bootstrap() { register_callbacks(); }
 }

test_regress/t/t_flag_main_vpi_lib2.cpp

@@ -19,7 +19,7 @@
 
 static void lib2_startup() { vpi_printf(const_cast<char*>("- second VPI library loaded\n")); }
 
-// IEEE 1800 §37: vlog_startup_routines[] — null-terminated array of startup functions
+// IEEE 1800 section 37: vlog_startup_routines[] -- null-terminated array of startup functions
 extern "C" {
 void (*vlog_startup_routines[])() = {lib2_startup, nullptr};
 }