Export of internal Abseil changes.

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2d7c9650fe2b1bf76085a993285e49db4d24aa4f by Derek Mauro <dmauro@google.com>:

Fix a build error in hash_test.cc under MSVC 2017

PiperOrigin-RevId: 249666534

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66887d4ed411663f688fc9852701d648fe7cefe6 by Derek Mauro <dmauro@google.com>:

Merge GitHub #316 - Avoid undefined behavior when passing nullptr to
memcpy with size 0.

Fixes #315

PiperOrigin-RevId: 249570899
GitOrigin-RevId: 2d7c9650fe2b1bf76085a993285e49db4d24aa4f
Change-Id: I0fae0c581f3c0df9e6f70c69661973d020155738

absl/hash/hash_test.cc

@@ -524,6 +524,7 @@ struct MinTag<a> : InvokeTagConstant<a> {};
 
 template <InvokeTag... Tags>
 struct CustomHashType {
+  explicit CustomHashType(size_t val) : value(val) {}
   size_t value;
 };
 
@@ -590,7 +591,7 @@ void TestCustomHashType(InvokeTagConstant<InvokeTag::kNone>, T...) {
   EXPECT_TRUE(is_hashable<const type&>());
 
   const size_t offset = static_cast<int>(std::min({T::value...}));
-  EXPECT_EQ(SpyHash(type{7}), SpyHash(size_t{7 + offset}));
+  EXPECT_EQ(SpyHash(type(7)), SpyHash(size_t{7 + offset}));
 }
 
 void TestCustomHashType(InvokeTagConstant<InvokeTag::kNone>) {