Made to compile by MSVC 2015/2017 32 bit compilers (#101)

Patches by @anatoly-spb :
1. Get rid of -DWIN64, -DZLIB_WINAPI in 32-bit build for fixing zlib linkage;
2. Work around MSVC2015 limitation based on lacking the C++14 features (like void as literal type) and document it.

Telegram/CMakeLists.txt

@@ -582,9 +582,9 @@ endif()
 
 if (WIN32)
     add_definitions(-D_CRT_SECURE_NO_WARNINGS -D_SCL_SECURE_NO_WARNINGS -D_USING_V110_SDK71_
-        -DWIN32 -D_WINDOWS -D_UNICODE -DUNICODE -DWIN64
+        -DWIN32 -D_WINDOWS -D_UNICODE -DUNICODE 
         -DWINAPI_FAMILY=WINAPI_FAMILY_DESKTOP_APP
-        -DHAVE_STDINT_H -DZLIB_WINAPI)
+        -DHAVE_STDINT_H)
 endif()
 
 add_definitions(-DAL_LIBTYPE_STATIC)

Telegram/SourceFiles/base/assertion.h

@@ -43,10 +43,17 @@ inline constexpr void noop() {
 	std::abort();
 }
 
-inline constexpr void validate(bool condition, const char *message, const char *file, int line) {
+// Since MSVC 2015 cannot understand "constexpr void" (void is literal since C++14)
+// we have to use conditional compilation 
+inline
+#if !defined(_MSC_VER) || (_MSC_VER > 1900)
+constexpr
+#endif
+  void validate(bool condition, const char *message, const char *file, int line) {
 	(GSL_UNLIKELY(!(condition))) ? fail(message, file, line) : noop();
 }
 
+
 } // namespace assertion
 } // namespace base
 

Telegram/SourceFiles/core/basic_types.h

@@ -54,4 +54,4 @@ void as_const(const T&&) = delete;
 #include <cstdint>
 
 #define qsl(s) QStringLiteral(s)
-#define qstr(s) QLatin1String(s, sizeof(s) - 1)
+#define qstr(s) QLatin1String(s, static_cast<int>(sizeof(s)-1))