fd-util: Move O_ACCMODE_STRICT to fd-util.h

We're still discussing whether we want to remove this or not, but
regardless of whether we end up removing it or not, it's something
we add ourselves and as such should not live in our headers that
override glibc headers, so let's move it to fd-util.h.

src/basic/fd-util.h

@@ -44,6 +44,12 @@
 #  endif
 #endif
 
+/* On musl, O_ACCMODE is defined as (03|O_SEARCH), unlike glibc which defines it as
+ * (O_RDONLY|O_WRONLY|O_RDWR). Additionally, O_SEARCH is simply defined as O_PATH. This changes the behaviour
+ * of O_ACCMODE in certain situations, which we don't want. This definition is copied from glibc and works
+ * around the problems with musl's definition. */
+#define O_ACCMODE_STRICT (O_RDONLY|O_WRONLY|O_RDWR)
+
 int close_nointr(int fd);
 int safe_close(int fd);
 void safe_close_pair(int p[static 2]);

src/basic/include/fcntl.h

@@ -17,9 +17,3 @@
 #ifndef AT_HANDLE_FID
 #define AT_HANDLE_FID AT_REMOVEDIR
 #endif
-
-/* On musl, O_ACCMODE is defined as (03|O_SEARCH), unlike glibc which defines it as
- * (O_RDONLY|O_WRONLY|O_RDWR). Additionally, O_SEARCH is simply defined as O_PATH. This changes the behaviour
- * of O_ACCMODE in certain situations, which we don't want. This definition is copied from glibc and works
- * around the problems with musl's definition. */
-#define O_ACCMODE_STRICT (O_RDONLY|O_WRONLY|O_RDWR)