Make the project build with Microsoft's broken C compiler.

MSVC is not fully C11-compliant, even when compiling with /std:c11.
Some changes were needed to make the codebase compatible. Notably, the
notation a[static N] and a[n] for function parameters of array type is
not supported, so that had to be hidden behind a macro.  Atomic types
are also an experimental feature, apparently, but at least they work
with the correct compiler flag.

One thing that MSVC does well, however, is warning on integer conversions
on /W4 level. I am not sure if Clang and GCC have something similar,
so I took this chance to fix some of these.

1 files changed, 14 insertions, 3 deletions

diff --git a/src/utils/compilers.h b/src/utils/compilers.h
index a7d6df5..1b175bb 100644
--- a/src/utils/compilers.h
+++ b/src/utils/compilers.h
@@ -1,13 +1,24 @@
 #if defined(__GNUC__)
 
-#define unused __attribute__((unused))
+#define UNUSED __attribute__((unused))
+#define SIZE(x) static (x)
+#define NON_NULL SIZE(1)
 
 #elif defined(__clang__)
 
-#define unused __attribute__((unused))
+#define UNUSED __attribute__((unused))
+#define SIZE(x) static (x)
+#define NON_NULL SIZE(1)
 
 #else
 
-#define unused
+/*
+For example MSVC, which is not fully C11 compliant (e.g. it does not support
+a[static N] notation for array parameters).
+*/
+
+#define UNUSED
+#define SIZE(x)
+#define NON_NULL
 
 #endif