[libc++][Android] Restrict use of mblen/towctrans/wctrans

These functions weren't added until API 26 (Android 8.0), but libc++ is
supported for API 21 and up.

These APIs are undeclared as of r.android.com/3216959.

Author: rprichard

libcxx/test/std/depr/depr.c.headers/stdlib_h.pass.cpp

@@ -141,7 +141,10 @@ int main(int, char**) {
     wchar_t* pw = 0;
     const wchar_t* pwc = 0;
     char* pc = 0;
+    // mblen was added in Android API 26.
+#if !defined(__ANDROID__) || __ANDROID_API__ >= 26
     ASSERT_SAME_TYPE(int,    decltype(mblen("",0)));
+#endif
     ASSERT_SAME_TYPE(int,    decltype(mbtowc(pw,"",0)));
     ASSERT_SAME_TYPE(int,    decltype(wctomb(pc,L' ')));
     ASSERT_SAME_TYPE(size_t, decltype(mbstowcs(pw,"",0)));

libcxx/test/std/depr/depr.c.headers/wctype_h.compile.pass.cpp

@@ -109,5 +109,8 @@ ASSERT_SAME_TYPE(int,       decltype(iswctype(w, wct)));
 ASSERT_SAME_TYPE(wctype_t,  decltype(wctype("")));
 ASSERT_SAME_TYPE(wint_t,    decltype(towlower(w)));
 ASSERT_SAME_TYPE(wint_t,    decltype(towupper(w)));
+// towctrans and wctrans were added in Android API 26.
+#if !defined(__ANDROID__) || __ANDROID_API__ >= 26
 ASSERT_SAME_TYPE(wint_t,    decltype(towctrans(w, wctr)));
 ASSERT_SAME_TYPE(wctrans_t, decltype(wctrans("")));
+#endif

libcxx/test/std/language.support/support.runtime/cstdlib.pass.cpp

@@ -141,7 +141,10 @@ int main(int, char**)
     wchar_t* pw = 0;
     const wchar_t* pwc = 0;
     char* pc = 0;
+    // mblen was added in Android API 26.
+#if !defined(__ANDROID__) || __ANDROID_API__ >= 26
     static_assert((std::is_same<decltype(std::mblen("",0)), int>::value), "");
+#endif
     static_assert((std::is_same<decltype(std::mbtowc(pw,"",0)), int>::value), "");
     static_assert((std::is_same<decltype(std::wctomb(pc,L' ')), int>::value), "");
     static_assert((std::is_same<decltype(std::mbstowcs(pw,"",0)), std::size_t>::value), "");

libcxx/test/std/strings/c.strings/cwctype.pass.cpp

@@ -111,8 +111,11 @@ int main(int, char**) {
   ASSERT_SAME_TYPE(std::wctype_t, decltype(std::wctype("")));
   ASSERT_SAME_TYPE(std::wint_t, decltype(std::towlower(w)));
   ASSERT_SAME_TYPE(std::wint_t, decltype(std::towupper(w)));
+  // towctrans and wctrans were added in Android API 26.
+#if !defined(__ANDROID__) || __ANDROID_API__ >= 26
   ASSERT_SAME_TYPE(std::wint_t, decltype(std::towctrans(w, std::wctrans_t())));
   ASSERT_SAME_TYPE(std::wctrans_t, decltype(std::wctrans("")));
+#endif
 
   return 0;
 }