Fixes for pre-C++11 compilers.

That said, I think we can consider upgrading requirement to an early VS-friendly subset of C++11. The thing I would like the most from C++11 are forward-declared enum (from VS 2012 onward).

imgui.h

@@ -117,11 +117,15 @@ typedef void (*ImGuiSizeCallback)(ImGuiSizeCallbackData* data);
 typedef signed int          ImS32;  // 32-bit signed integer == int
 typedef unsigned int        ImU32;  // 32-bit unsigned integer (often used to store packed colors)
 #if defined(_MSC_VER) && !defined(__clang__)
-typedef signed   __int64    ImS64;  // 64-bit signed integer
+typedef signed   __int64    ImS64;  // 64-bit signed integer (pre and post C++11 with Visual Studio)
-typedef unsigned __int64    ImU64;  // 64-bit unsigned integer
+typedef unsigned __int64    ImU64;  // 64-bit unsigned integer (pre and post C++11 with Visual Studio)
+#elif (defined(__clang__) || defined(__GNUC__)) && (__cplusplus < 201100)
+#include <stdint.h>
+typedef int64_t             ImS64;  // 64-bit signed integer (pre C++11)
+typedef uint64_t            ImU64;  // 64-bit unsigned integer (pre C++11)
 #else
-typedef signed   long long  ImS64;  // 64-bit signed integer
+typedef signed   long long  ImS64;  // 64-bit signed integer (post C++11)
-typedef unsigned long long  ImU64;  // 64-bit unsigned integer
+typedef unsigned long long  ImU64;  // 64-bit unsigned integer (post C++11)
 #endif
 
 // 2D vector (often used to store positions, sizes, etc.)

imgui_demo.cpp

@@ -1035,7 +1035,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
             const ImS64   s64_zero = 0,   s64_one = 1,   s64_fifty = 50, s64_min = LLONG_MIN/2, s64_max = LLONG_MAX/2,  s64_hi_a = LLONG_MAX/2 - 100,  s64_hi_b = LLONG_MAX/2;
             const ImU64   u64_zero = 0,   u64_one = 1,   u64_fifty = 50, u64_min = 0,           u64_max = ULLONG_MAX/2, u64_hi_a = ULLONG_MAX/2 - 100, u64_hi_b = ULLONG_MAX/2;
             const float   f32_zero = 0.f, f32_one = 1.f, f32_lo_a = -10000000000.0f, f32_hi_a = +10000000000.0f;
-            const double  f64_zero = 0.,  f64_one = 1.,  f64_lo_a = -1000000000000000, f64_hi_a = +1000000000000000;
+            const double  f64_zero = 0.,  f64_one = 1.,  f64_lo_a = -1000000000000000.0, f64_hi_a = +1000000000000000.0;
 
             // State
             static ImS32  s32_v = -1;