Set V8_HAS_DECLSPEC_SELECTANY for clang-cl

This macro is used for defining static data members with
STATIC_CONST_MEMBER_DEFINITION. Clang-cl mimics MSVC's
behaviour here, so it also needs __declspec(selectany).

This change was prompted by Clang r237787 which changed
a bug where Clang would previously not emit symbols for
some static data members.

BUG=82385
LOG=N

Review URL: https://codereview.chromium.org/1145213004

Cr-Commit-Position: refs/heads/master@{#28563}

include/v8config.h

@@ -199,8 +199,6 @@
 
 #if defined(__GNUC__)  // Clang in gcc mode.
 # define V8_CC_GNU 1
-#elif defined(_MSC_VER)  // Clang in cl mode.
-# define V8_CC_MSVC 1
 #endif
 
 // Clang defines __alignof__ as alias for __alignof
@@ -268,11 +266,10 @@
 #  define V8_HAS_CXX11_ALIGNOF (V8_GNUC_PREREQ(4, 8, 0))
 #  define V8_HAS_CXX11_STATIC_ASSERT (V8_GNUC_PREREQ(4, 3, 0))
 # endif
+#endif
 
-#elif defined(_MSC_VER)
-
+#if defined(_MSC_VER)
 # define V8_CC_MSVC 1
-
 # define V8_HAS___ALIGNOF 1
 
 # define V8_HAS_DECLSPEC_ALIGN 1