make poll available for other platforms lacking it

move poll.[ch] out of compat/win32/ into compat/poll/ and adjust
Makefile with the changed paths. Adding comments to Makefile about
how/when to enable it and add logic for this

Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -154,6 +154,11 @@ all::
 #
 # Define NO_MMAP if you want to avoid mmap.
 #
+# 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.
+#
 # Define NO_PTHREADS if you do not have or do not want to use Pthreads.
 #
 # Define NO_PREAD if you have a problem with pread() system call (e.g.
@@ -603,10 +608,10 @@ LIB_H += compat/bswap.h
 LIB_H += compat/cygwin.h
 LIB_H += compat/mingw.h
 LIB_H += compat/obstack.h
+LIB_H += compat/poll/poll.h
 LIB_H += compat/precompose_utf8.h
 LIB_H += compat/terminal.h
 LIB_H += compat/win32/dirent.h
-LIB_H += compat/win32/poll.h
 LIB_H += compat/win32/pthread.h
 LIB_H += compat/win32/syslog.h
 LIB_H += connected.h
@@ -1224,7 +1229,7 @@ ifeq ($(uname_S),Windows)
 	NO_PREAD = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
-	NO_SYS_POLL_H = YesPlease
+	NO_POLL = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NO_IPV6 = YesPlease
 	NO_UNIX_SOCKETS = YesPlease
@@ -1265,7 +1270,7 @@ ifeq ($(uname_S),Windows)
 	BASIC_CFLAGS = -nologo -I. -I../zlib -Icompat/vcbuild -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
 	COMPAT_OBJS = compat/msvc.o compat/winansi.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
-		compat/win32/poll.o compat/win32/dirent.o
+		compat/win32/dirent.o
 	COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DNOGDI -DHAVE_STRING_H -DHAVE_ALLOCA_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
 	BASIC_LDFLAGS = -IGNORE:4217 -IGNORE:4049 -NOLOGO -SUBSYSTEM:CONSOLE -NODEFAULTLIB:MSVCRT.lib
 	EXTLIBS = user32.lib advapi32.lib shell32.lib wininet.lib ws2_32.lib
@@ -1320,7 +1325,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	NO_PREAD = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
-	NO_SYS_POLL_H = YesPlease
+	NO_POLL = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NO_UNIX_SOCKETS = YesPlease
 	NO_SETENV = YesPlease
@@ -1355,7 +1360,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
 	COMPAT_OBJS += compat/mingw.o compat/winansi.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
-		compat/win32/poll.o compat/win32/dirent.o
+		compat/win32/dirent.o
 	EXTLIBS += -lws2_32
 	PTHREAD_LIBS =
 	X = .exe
@@ -1609,6 +1614,11 @@ ifdef NO_GETTEXT
 	BASIC_CFLAGS += -DNO_GETTEXT
 	USE_GETTEXT_SCHEME ?= fallthrough
 endif
+ifdef NO_POLL
+	NO_SYS_POLL_H = YesPlease
+	COMPAT_CFLAGS += -DNO_POLL -Icompat/poll
+	COMPAT_OBJS += compat/poll/poll.o
+endif
 ifdef NO_STRCASESTR
 	COMPAT_CFLAGS += -DNO_STRCASESTR
 	COMPAT_OBJS += compat/strcasestr.o