Fix std::wstring capacity test for short wchar_t

	* testsuite/21_strings/basic_string/capacity/char/18654.cc: Use
	real minimum capacity.
	* testsuite/21_strings/basic_string/capacity/wchar_t/18654.cc:
	Likewise.

From-SVN: r230378

libstdc++-v3/ChangeLog

+2015-11-14  Jonathan Wakely  <jwakely@redhat.com>
+
+	* testsuite/21_strings/basic_string/capacity/char/18654.cc: Use
+	real minimum capacity.
+	* testsuite/21_strings/basic_string/capacity/wchar_t/18654.cc:
+	Likewise.
+
 2015-11-13  David Edelsohn  <dje.gcc@gmail.com>
 
 	* testsuite/experimental/random/randint.cc: Add dg-add-options tls.

libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/18654.cc

@@ -38,7 +38,7 @@ void test01()
 
 #if _GLIBCXX_USE_CXX11_ABI
   // Can't shrink below small string size.
-  const size_type minsize = 2 << 3;
+  const size_type minsize = string().capacity() + 1;
 #else
   // Exact shrink-to-size and shrink-to-fit
   const size_type minsize = 2 << 0;

libstdc++-v3/testsuite/21_strings/basic_string/capacity/wchar_t/18654.cc

@@ -38,7 +38,7 @@ void test01()
 
 #if _GLIBCXX_USE_CXX11_ABI
   // Can't shrink below small string size.
-  const size_type minsize = 2 << 1;
+  const size_type minsize = wstring().capacity() + 1;
 #else
   // Exact shrink-to-size and shrink-to-fit
   const size_type minsize = 2 << 0;