Move Abseil to C++14 minimum

Adds policy checks the raise the minimum C++ version to C++14
and the minimum GCC version to GCC 5

Updates the docs to indicate the C++14 minimum.

PiperOrigin-RevId: 459401288
Change-Id: I18878f0e13001c57e97e26ad7c9a9c9c12c39265

1 files changed, 12 insertions, 10 deletions

diff --git a/absl/base/policy_checks.h b/absl/base/policy_checks.h
index 06b32439..d13073c8 100644
--- a/absl/base/policy_checks.h
+++ b/absl/base/policy_checks.h
@@ -50,11 +50,11 @@
 #error "This package requires Visual Studio 2015 Update 2 or higher."
 #endif
 
-// We support gcc 4.7 and later.
+// We support gcc 5 and later.
 // This minimum will go up.
 #if defined(__GNUC__) && !defined(__clang__)
-#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 7)
-#error "This package requires gcc 4.7 or higher."
+#if __GNUC__ < 5
+#error "This package requires gcc 5 or higher."
 #endif
 #endif
 
@@ -69,13 +69,15 @@
 // C++ Version Check
 // -----------------------------------------------------------------------------
 
-// Enforce C++11 as the minimum.  Note that Visual Studio has not
-// advanced __cplusplus despite being good enough for our purposes, so
-// so we exempt it from the check.
-#if defined(__cplusplus) && !defined(_MSC_VER)
-#if __cplusplus < 201103L
-#error "C++ versions less than C++11 are not supported."
-#endif
+// Enforce C++14 as the minimum.
+#if defined(_MSVC_LANG)
+#if _MSVC_LANG < 201402L
+#error "C++ versions less than C++14 are not supported."
+#endif  // _MSVC_LANG < 201402L
+#elif defined(__cplusplus)
+#if __cplusplus < 201402L
+#error "C++ versions less than C++14 are not supported."
+#endif  // __cplusplus < 201402L
 #endif
 
 // -----------------------------------------------------------------------------