test: Rename string_op+= to string_op_plus_equal. Windows git doesn't like it.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@121265 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/strings/basic.string/string.modifiers/string_op+=/char.pass.cpp b/test/strings/basic.string/string.modifiers/string_op_plus_equal/char.pass.cpp
similarity index 100%
rename from test/strings/basic.string/string.modifiers/string_op+=/char.pass.cpp
rename to test/strings/basic.string/string.modifiers/string_op_plus_equal/char.pass.cpp
diff --git a/test/strings/basic.string/string.modifiers/string_op+=/initializer_list.pass.cpp b/test/strings/basic.string/string.modifiers/string_op_plus_equal/initializer_list.pass.cpp
similarity index 100%
rename from test/strings/basic.string/string.modifiers/string_op+=/initializer_list.pass.cpp
rename to test/strings/basic.string/string.modifiers/string_op_plus_equal/initializer_list.pass.cpp
diff --git a/test/strings/basic.string/string.modifiers/string_op+=/pointer.pass.cpp b/test/strings/basic.string/string.modifiers/string_op_plus_equal/pointer.pass.cpp
similarity index 100%
rename from test/strings/basic.string/string.modifiers/string_op+=/pointer.pass.cpp
rename to test/strings/basic.string/string.modifiers/string_op_plus_equal/pointer.pass.cpp
diff --git a/test/strings/basic.string/string.modifiers/string_op+=/string.pass.cpp b/test/strings/basic.string/string.modifiers/string_op_plus_equal/string.pass.cpp
similarity index 100%
rename from test/strings/basic.string/string.modifiers/string_op+=/string.pass.cpp
rename to test/strings/basic.string/string.modifiers/string_op_plus_equal/string.pass.cpp