LibCore+LibC: Add wrapper for setenv

I also added a common interface with StringView compatible parameters:

int serenity_setenv(const char*, ssize_t, const char*, ssize_t, int)

This function is called by both C and C++ API for setenv().

Userland/Libraries/LibC/stdlib.cpp

@@ -305,12 +305,17 @@ int clearenv()
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/setenv.html
 int setenv(const char* name, const char* value, int overwrite)
+{
+    return serenity_setenv(name, strlen(name), value, strlen(value), overwrite);
+}
+
+int serenity_setenv(const char* name, ssize_t name_length, const char* value, ssize_t value_length, int overwrite)
 {
     if (!overwrite && getenv(name))
         return 0;
-    auto length = strlen(name) + strlen(value) + 2;
+    auto const total_length = name_length + value_length + 2;
-    auto* var = (char*)malloc(length);
+    auto* var = (char*)malloc(total_length);
-    snprintf(var, length, "%s=%s", name, value);
+    snprintf(var, total_length, "%s=%s", name, value);
     s_malloced_environment_variables.set((FlatPtr)var);
     return putenv(var);
 }

Userland/Libraries/LibC/stdlib.h

@@ -33,6 +33,7 @@ int putenv(char*);
 int unsetenv(const char*);
 int clearenv(void);
 int setenv(const char* name, const char* value, int overwrite);
+int serenity_setenv(const char* name, ssize_t name_length, const char* value, ssize_t value_length, int overwrite);
 const char* getprogname(void);
 void setprogname(const char*);
 int atoi(const char*);

Userland/Libraries/LibCore/System.cpp

@@ -14,6 +14,7 @@
 #include <LibSystem/syscall.h>
 #include <limits.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/ptrace.h>
@@ -1069,4 +1070,18 @@ ErrorOr<void> mkfifo(StringView pathname, mode_t mode)
     return mknod(pathname, mode | S_IFIFO, 0);
 }
 
+ErrorOr<void> setenv(StringView name, StringView value, bool overwrite)
+{
+#ifdef __serenity__
+    auto const rc = ::serenity_setenv(name.characters_without_null_termination(), name.length(), value.characters_without_null_termination(), value.length(), overwrite);
+#else
+    String name_string = name;
+    String value_string = value;
+    auto const rc = ::setenv(name_string.characters(), value_string.characters(), overwrite);
+#endif
+    if (rc < 0)
+        return Error::from_syscall("setenv", -errno);
+    return {};
+}
+
 }

Userland/Libraries/LibCore/System.h

@@ -145,4 +145,6 @@ ErrorOr<void> socketpair(int domain, int type, int protocol, int sv[2]);
 ErrorOr<Vector<gid_t>> getgroups();
 ErrorOr<void> mknod(StringView pathname, mode_t mode, dev_t dev);
 ErrorOr<void> mkfifo(StringView pathname, mode_t mode);
+ErrorOr<void> setenv(StringView, StringView, bool);
+
 }