git-compat-util: prefer poll.h to sys/poll.h

POSIX specifies that <poll.h> is the correct header for poll(2)
whereas <sys/poll.h> is only needed for some old libc.

Let's follow the POSIX way by default.

This effectively eliminates musl's warning:

    warning redirecting incorrect #include <sys/poll.h> to <poll.h>

Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -207,10 +207,12 @@ all::
 # Define MMAP_PREVENTS_DELETE if a file that is currently mmapped cannot be
 # deleted or cannot be replaced using rename().
 #
+# Define NO_POLL_H if you don't have poll.h.
+#
 # Define NO_SYS_POLL_H if you don't have sys/poll.h.
 #
 # Define NO_POLL if you do not have or don't want to use poll().
-# This also implies NO_SYS_POLL_H.
+# This also implies NO_POLL_H and NO_SYS_POLL_H.
 #
 # Define NEEDS_SYS_PARAM_H if you need to include sys/param.h to compile,
 # *PLEASE* REPORT to git@vger.kernel.org if your platform needs this;
@@ -1460,6 +1462,7 @@ ifdef NO_GETTEXT
 	USE_GETTEXT_SCHEME ?= fallthrough
 endif
 ifdef NO_POLL
+	NO_POLL_H = YesPlease
 	NO_SYS_POLL_H = YesPlease
 	COMPAT_CFLAGS += -DNO_POLL -Icompat/poll
 	COMPAT_OBJS += compat/poll/poll.o
@@ -1498,6 +1501,9 @@ endif
 ifdef NO_SYS_SELECT_H
 	BASIC_CFLAGS += -DNO_SYS_SELECT_H
 endif
+ifdef NO_POLL_H
+	BASIC_CFLAGS += -DNO_POLL_H
+endif
 ifdef NO_SYS_POLL_H
 	BASIC_CFLAGS += -DNO_SYS_POLL_H
 endif

configure.ac

@@ -792,6 +792,12 @@ AC_CHECK_HEADER([sys/select.h],
 [NO_SYS_SELECT_H=UnfortunatelyYes])
 GIT_CONF_SUBST([NO_SYS_SELECT_H])
 #
+# Define NO_POLL_H if you don't have poll.h
+AC_CHECK_HEADER([poll.h],
+[NO_POLL_H=],
+[NO_POLL_H=UnfortunatelyYes])
+GIT_CONF_SUBST([NO_POLL_H])
+#
 # Define NO_SYS_POLL_H if you don't have sys/poll.h
 AC_CHECK_HEADER([sys/poll.h],
 [NO_SYS_POLL_H=],

git-compat-util.h

@@ -180,9 +180,12 @@
 #include <regex.h>
 #include <utime.h>
 #include <syslog.h>
-#ifndef NO_SYS_POLL_H
+#if !defined(NO_POLL_H)
+#include <poll.h>
+#elif !defined(NO_SYS_POLL_H)
 #include <sys/poll.h>
 #else
+/* Pull the compat stuff */
 #include <poll.h>
 #endif
 #ifdef HAVE_BSD_SYSCTL