libc: isolate guest setenv from host environment. Fix linux debugging

.vscode/launch.json

@@ -37,8 +37,16 @@
                 "type": "cppdbg",
                 "program": "${workspaceFolder}/_Build/vscode-clang/kyty_emulator",
                 "cwd": "${workspaceFolder}/_Build/vscode-clang",
+                "externalConsole": false,
                 "MIMode": "gdb",
-                "miDebuggerPath": "/usr/bin/gdb"
+                "miDebuggerPath": "/usr/bin/gdb",
+                "setupCommands": [
+                    {
+                        "description": "Pass Kyty's internal signals to its handlers",
+                        "text": "handle SIG37 SIGSEGV SIGBUS SIGILL nostop noprint pass",
+                        "ignoreFailures": false
+                    }
+                ]
             }
         },
         {
@@ -49,7 +57,14 @@
             "linux": {
                 "type": "cppdbg",
                 "MIMode": "gdb",
-                "miDebuggerPath": "/usr/bin/gdb"
+                "miDebuggerPath": "/usr/bin/gdb",
+                "setupCommands": [
+                    {
+                        "description": "Pass Kyty's internal signals to its handlers",
+                        "text": "handle SIG37 SIGSEGV SIGBUS SIGILL nostop noprint pass",
+                        "ignoreFailures": false
+                    }
+                ]
             }
         }
     ]

src/libs/libC.cpp

@@ -327,25 +327,8 @@ static KYTY_SYSV_ABI int setenv(const char* name, const char* value, int overwri
 		return -1;
 	}
 
-	if (overwrite == 0 && std::getenv(name) != nullptr) {
+	// Guest environment changes must not leak into emulator host libraries.
-		return 0;
-	}
-
-#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
-	const auto ret = ::_putenv_s(name, value);
-	if (ret != 0) {
-		*Posix::GetErrorAddr() = ret;
-		return -1;
-	}
 	return 0;
-#else
-	const auto ret = ::setenv(name, value, overwrite);
-	if (ret != 0) {
-		*Posix::GetErrorAddr() = errno;
-		return -1;
-	}
-	return 0;
-#endif
 }
 
 static KYTY_SYSV_ABI int64_t libc_time(int64_t* timer) {