compat/*.[ch]: remove extern from function declarations using spatch

In 5545442 (*.[ch]: remove extern from function declarations using
spatch, 2019-04-29), we removed externs from function declarations using
spatch but we intentionally excluded files under compat/ since some are
directly copied from an upstream and we should avoid churning them so
that manually merging future updates will be simpler.

In the last commit, we determined the files which taken from an upstream
so we can exclude them and run spatch on the remainder.

This was the Coccinelle patch used:

	@@
	type T;
	identifier f;
	@@
	- extern
	  T f(...);

and it was run with:

	$ git ls-files compat/\*\*.{c,h} |
		xargs spatch --sp-file contrib/coccinelle/noextern.cocci --in-place
	$ git checkout -- \
		compat/regex/ \
		compat/inet_ntop.c \
		compat/inet_pton.c \
		compat/nedmalloc/ \
		compat/obstack.{c,h} \
		compat/poll/

Coccinelle has some trouble dealing with `__attribute__` and varargs so
we ran the following to ensure that no remaining changes were left
behind:

	$ git ls-files compat/\*\*.{c,h} |
		xargs sed -i'' -e 's/^\(\s*\)extern \([^(]*([^*]\)/\1\2/'
	$ git checkout -- \
		compat/regex/ \
		compat/inet_ntop.c \
		compat/inet_pton.c \
		compat/nedmalloc/ \
		compat/obstack.{c,h} \
		compat/poll/

Signed-off-by: Denton Liu <[email protected]>
Acked-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Denton-L

compat/mingw.h

@@ -11,7 +11,7 @@ typedef _sigset_t sigset_t;
 #undef _POSIX_THREAD_SAFE_FUNCTIONS
 #endif
 
-extern int mingw_core_config(const char *var, const char *value, void *cb);
+int mingw_core_config(const char *var, const char *value, void *cb);
 #define platform_core_config mingw_core_config
 
 /*
@@ -443,7 +443,7 @@ static inline void convert_slashes(char *path)
 			*path = '/';
 }
 #define PATH_SEP ';'
-extern char *mingw_query_user_email(void);
+char *mingw_query_user_email(void);
 #define query_user_email mingw_query_user_email
 #if !defined(__MINGW64_VERSION_MAJOR) && (!defined(_MSC_VER) || _MSC_VER < 1800)
 #define PRIuMAX "I64u"
@@ -580,4 +580,4 @@ int main(int argc, const char **argv);
 /*
  * Used by Pthread API implementation for Windows
  */
-extern int err_win_to_posix(DWORD winerr);
+int err_win_to_posix(DWORD winerr);

compat/win32/pthread.h

@@ -50,7 +50,7 @@ typedef struct {
 	DWORD tid;
 } pthread_t;
 
-extern int pthread_create(pthread_t *thread, const void *unused,
+int pthread_create(pthread_t *thread, const void *unused,
 			  void *(*start_routine)(void*), void *arg);
 
 /*
@@ -59,10 +59,10 @@ extern int pthread_create(pthread_t *thread, const void *unused,
  */
 #define pthread_join(a, b) win32_pthread_join(&(a), (b))
 
-extern int win32_pthread_join(pthread_t *thread, void **value_ptr);
+int win32_pthread_join(pthread_t *thread, void **value_ptr);
 
 #define pthread_equal(t1, t2) ((t1).tid == (t2).tid)
-extern pthread_t pthread_self(void);
+pthread_t pthread_self(void);
 
 static inline void NORETURN pthread_exit(void *ret)
 {