Add an internal ASSERT macro

This macro has some advantages over the standard library one:
 - It prints the place where the macro was triggered
 - It "references" the condition even in Release to avoid warnings
 - In release, if possible, it gives compiler hints

It is basically is stripped down version of the ASSERT macros I wrote
for the Daemon engine in src/common/Assert.h

This commit also removes the stray "backend" namespaces for common/
code.

src/common/Math.cpp

@@ -14,53 +14,48 @@
 
 #include "common/Math.h"
 
+#include "common/Assert.h"
+
 #if defined(_WIN32) || defined(_WIN64)
     #include <intrin.h>
 #endif
 
-#include <cassert>
-#define ASSERT assert
-
-namespace backend {
-
-    uint32_t ScanForward(uint32_t bits) {
-        ASSERT(bits != 0);
-        #if defined(_WIN32) || defined(_WIN64)
-            unsigned long firstBitIndex = 0ul;
-            unsigned char ret = _BitScanForward(&firstBitIndex, bits);
-            ASSERT(ret != 0);
-            return firstBitIndex;
-        #else
-            return static_cast<unsigned long>(__builtin_ctz(bits));
-        #endif
-    }
-
-    uint32_t Log2(uint32_t value) {
-        ASSERT(value != 0);
-        #if defined(_WIN32) || defined(_WIN64)
-            unsigned long firstBitIndex = 0ul;
-            unsigned char ret = _BitScanReverse(&firstBitIndex, value);
-            ASSERT(ret != 0);
-            return firstBitIndex;
-        #else
-            return 31 - __builtin_clz(value);
-        #endif
-    }
-
-    bool IsPowerOfTwo(size_t n) {
-        ASSERT(n != 0);
-        return (n & (n - 1)) == 0;
-    }
-
-    bool IsAligned(const void* ptr, size_t alignment) {
-        ASSERT(IsPowerOfTwo(alignment));
-        ASSERT(alignment != 0);
-        return (reinterpret_cast<intptr_t>(ptr) & (alignment - 1)) == 0;
-    }
-
-    void* AlignVoidPtr(void* ptr, size_t alignment) {
-        ASSERT(alignment != 0);
-        return reinterpret_cast<void*>((reinterpret_cast<intptr_t>(ptr) + (alignment - 1)) & ~(alignment - 1));
-    }
-
+uint32_t ScanForward(uint32_t bits) {
+    ASSERT(bits != 0);
+    #if defined(_WIN32) || defined(_WIN64)
+        unsigned long firstBitIndex = 0ul;
+        unsigned char ret = _BitScanForward(&firstBitIndex, bits);
+        ASSERT(ret != 0);
+        return firstBitIndex;
+    #else
+        return static_cast<unsigned long>(__builtin_ctz(bits));
+    #endif
+}
+
+uint32_t Log2(uint32_t value) {
+    ASSERT(value != 0);
+    #if defined(_WIN32) || defined(_WIN64)
+        unsigned long firstBitIndex = 0ul;
+        unsigned char ret = _BitScanReverse(&firstBitIndex, value);
+        ASSERT(ret != 0);
+        return firstBitIndex;
+    #else
+        return 31 - __builtin_clz(value);
+    #endif
+}
+
+bool IsPowerOfTwo(size_t n) {
+    ASSERT(n != 0);
+    return (n & (n - 1)) == 0;
+}
+
+bool IsAligned(const void* ptr, size_t alignment) {
+    ASSERT(IsPowerOfTwo(alignment));
+    ASSERT(alignment != 0);
+    return (reinterpret_cast<intptr_t>(ptr) & (alignment - 1)) == 0;
+}
+
+void* AlignVoidPtr(void* ptr, size_t alignment) {
+    ASSERT(alignment != 0);
+    return reinterpret_cast<void*>((reinterpret_cast<intptr_t>(ptr) + (alignment - 1)) & ~(alignment - 1));
 }