compat-util: type-check parameters of no-op replacement functions

When there is no need to run a specific function on certain platforms,
we often #define an empty function to swallow its parameters and
make it into a no-op, e.g.

    #define precompose_argv(c,v) /* no-op */

While this guarantees that no unneeded code is generated, it also
discards type and other checks on these parameters, e.g. a new code
written with the argv-array API (diff_args is of type "struct
argv_array" that has .argc and .argv members):

    precompose_argv(diff_args.argc, diff_args.argv);

must be updated to use "struct strvec diff_args" with .nr and .v
members, like so:

    precompose_argv(diff_args.nr, diff_args.v);

after the argv-array API has been updated to the strvec API.
However, the "no oop" C preprocessor macro is too aggressive to
discard what is unused, and did not catch such a call that was left
unconverted.

Using a "static inline" function whose body is a no-op should still
result in the same binary with decent compilers yet catch such a
reference to a missing field or passing a value of a wrong type.

While at it, I notice that precompute_str() has never been used
anywhere in the code, since it was introduced at 76759c7d (git on
Mac OS and precomposed unicode, 2012-07-08).  Instead of turning it
into a static inline, just remove it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -252,8 +252,10 @@ typedef unsigned long uintptr_t;
 #ifdef PRECOMPOSE_UNICODE
 #include "compat/precompose_utf8.h"
 #else
-#define precompose_str(in,i_nfd2nfc)
-#define precompose_argv(c,v)
+static inline void precompose_argv(int argc, const char **argv)
+{
+	; /* nothing */
+}
 #define probe_utf8_pathname_composition()
 #endif
 
@@ -270,7 +272,9 @@ struct itimerval {
 #endif
 
 #ifdef NO_SETITIMER
-#define setitimer(which,value,ovalue)
+static inline int setitimer(int which, const struct itimerval *value, struct itimerval *newvalue) {
+	; /* nothing */
+}
 #endif
 
 #ifndef NO_LIBGEN_H
@@ -1231,8 +1235,14 @@ int warn_on_fopen_errors(const char *path);
 #endif
 
 #ifndef _POSIX_THREAD_SAFE_FUNCTIONS
-#define flockfile(fh)
-#define funlockfile(fh)
+static inline void flockfile(FILE *fh)
+{
+	; /* nothing */
+}
+static inline void funlockfile(FILE *fh)
+{
+	; /* nothing */
+}
 #define getc_unlocked(fh) getc(fh)
 #endif