Change std to lstd in Target::isCXX11orNewer()

Apparently `std` seems to be reserved, as the compilation fails when using this name:
```
target.cpp:178:17: error: unexpected ':' in nested name specifier; did you mean '::'?
  for (auto std : STD) {
                ^
                ::
target.cpp:178:19: error: definition or redeclaration of 'STD' not allowed inside a function
  for (auto std : STD) {
            ~~~~~ ^
target.cpp:178:19: error: no member named 'STD' in namespace 'std'
  for (auto std : STD) {
            ~~~~~ ^
target.cpp:178:19: error: declaration of variable 'STD' with type 'auto' requires an initializer
target.cpp:178:22: error: expected ';' in 'for' statement specifier
  for (auto std : STD) {
                     ^
target.cpp:178:22: error: expected ';' in 'for' statement specifier
target.cpp:179:26: error: unexpected namespace name 'std': expected expression
    if (!strcmp(langstd, std))
```