Move QB64 compiler settings to libqb-common.h

This moves a lot of the preprocessor flags for what compiler/platform
we're using into a libqb-common.h header inside the libqb/include
folder. This gets included at the top of every libqb .cpp file, and is
intended to be fairly small, providing only necessary things like
_WIN32_WINNT (which needs to be defined before including <windows.h> or
friends).

internal/c/libqb/include/libqb-common.h

@@ -0,0 +1,54 @@
+#ifndef INCLUDE_LIBQB_LIBQB_COMMON_H
+#define INCLUDE_LIBQB_LIBQB_COMMON_H
+// Should be included at the top of every .cpp file
+
+/* Provide some OS/compiler macros.
+ * QB64_WINDOWS: Is this a Windows system?
+ * QB64_LINUX: Is this a Linux system?
+ * QB64_MACOSX: Is this MacOSX, or MacOS or whatever Apple calls it now?
+ * QB64_UNIX: Is this a Unix-flavoured system?
+ *
+ * QB64_BACKSLASH_FILESYSTEM: Does this system use \ for file paths (as opposed to /)?
+ * QB64_MICROSOFT: Are we compiling with Visual Studio?
+ * QB64_GCC: Are we compiling with gcc?
+ * QB64_MINGW: Are we compiling with MinGW, specifically? (Set in addition to QB64_GCC)
+ *
+ * QB64_32: A 32bit system (the default)
+ * QB64_64: A 64bit system (assumes all Macs are 64 bit)
+ */
+#ifdef WIN32
+#    define QB64_WINDOWS
+// This supports Windows Vista and up
+#    define _WIN32_WINNT 0x0600
+
+#    define QB64_BACKSLASH_FILESYSTEM
+#    ifdef _MSC_VER
+// Do we even support non-mingw compilers on Windows?
+#        define QB64_MICROSOFT
+#    else
+#        define QB64_GCC
+#        define QB64_MINGW
+#    endif
+#elif defined(__APPLE__)
+#    define QB64_MACOSX
+#    define QB64_UNIX
+#    define QB64_GCC
+#elif defined(__linux__)
+#    define QB64_LINUX
+#    define QB64_UNIX
+#    define QB64_GCC
+#else
+#    error "Unknown system; refusing to build. Edit os.h if needed"
+#endif
+
+#if defined(_WIN64) || defined(__x86_64__) || defined(__ppc64__) || defined(QB64_MACOSX) || defined(__aarch64__)
+#    define QB64_64
+#else
+#    define QB64_32
+#endif
+
+#if !defined(i386) && !defined(__x86_64__)
+#    define QB64_NOT_X86
+#endif
+
+#endif

internal/c/libqb/src/buffer.cpp

@@ -1,4 +1,6 @@
 
+#include "libqb-common.h"
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>

internal/c/libqb/src/threading-posix.cpp

@@ -1,4 +1,6 @@
 
+#include "libqb-common.h"
+
 #include <stdlib.h>
 #include <string.h>
 #include <pthread.h>

internal/c/libqb/src/threading-windows.cpp

@@ -1,6 +1,5 @@
 
-// FIXME: Move this to some kind of global header
-#define _WIN32_WINNT 0x0600
+#include "libqb-common.h"
 
 #include <windows.h>
 #include <synchapi.h>

internal/c/libqb/src/threading.cpp

@@ -1,4 +1,6 @@
 
+#include "libqb-common.h"
+
 #include "mutex.h"
 #include "condvar.h"
 #include "completion.h"

internal/c/os.h

@@ -1,48 +1,5 @@
-/* Provide some OS/compiler macros.
- * QB64_WINDOWS: Is this a Windows system?
- * QB64_LINUX: Is this a Linux system?
- * QB64_MACOSX: Is this MacOSX, or MacOS or whatever Apple calls it now?
- * QB64_UNIX: Is this a Unix-flavoured system?
- *
- * QB64_BACKSLASH_FILESYSTEM: Does this system use \ for file paths (as opposed to /)?
- * QB64_MICROSOFT: Are we compiling with Visual Studio?
- * QB64_GCC: Are we compiling with gcc?
- * QB64_MINGW: Are we compiling with MinGW, specifically? (Set in addition to QB64_GCC)
- *
- * QB64_32: A 32bit system (the default)
- * QB64_64: A 64bit system (assumes all Macs are 64 bit)
- */
-#ifdef WIN32
-#    define QB64_WINDOWS
-#    define QB64_BACKSLASH_FILESYSTEM
-#    ifdef _MSC_VER
-// Do we even support non-mingw compilers on Windows?
-#        define QB64_MICROSOFT
-#    else
-#        define QB64_GCC
-#        define QB64_MINGW
-#    endif
-#elif defined(__APPLE__)
-#    define QB64_MACOSX
-#    define QB64_UNIX
-#    define QB64_GCC
-#elif defined(__linux__)
-#    define QB64_LINUX
-#    define QB64_UNIX
-#    define QB64_GCC
-#else
-#    error "Unknown system; refusing to build. Edit os.h if needed"
-#endif
 
-#if defined(_WIN64) || defined(__x86_64__) || defined(__ppc64__) || defined(QB64_MACOSX) || defined(__aarch64__)
-#    define QB64_64
-#else
-#    define QB64_32
-#endif
-
-#if !defined(i386) && !defined(__x86_64__)
-#    define QB64_NOT_X86
-#endif
+#include "libqb-common.h"
 
 /* common types (not quite an include guard, but allows an including
  * file to not have these included.

internal/c/parts/audio/out/src/config.h

@@ -1,9 +1,4 @@
-#define QB64_OS_H_NO_TYPES
-#ifdef WIN32
- #include "..\..\..\..\os.h"
-#else
- #include "../../../../os.h"
-#endif
+#include "../../../../libqb/include/libqb-common.h"
 
 #ifndef CONFIG_H
 #define CONFIG_H