build system: drop PLATFORM_LINUX

PLATFORM_LINUX is a hidden configuration option which is disabled by
default and enabled at over a hundred locations for features that are
deemed to be Linux specific.

The only effect of PLATFORM_LINUX is to control compilation of
libbb/match_fstype.c.  This file is only needed by mount and umount.

Remove all references to PLATFORM_LINUX and compile match_fstype.c
if mount or umount is enabled.

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

modutils/depmod.c

@@ -10,7 +10,6 @@
 //config:config DEPMOD
 //config:	bool "depmod (27 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	depmod generates modules.dep (and potentially modules.alias
 //config:	and modules.symbols) that contain dependency information

modutils/insmod.c

@@ -9,7 +9,6 @@
 //config:config INSMOD
 //config:	bool "insmod (22 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	insmod is used to load specified modules in the running kernel.
 

modutils/lsmod.c

@@ -10,7 +10,6 @@
 //config:config LSMOD
 //config:	bool "lsmod (1.9 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	lsmod is used to display a list of loaded modules.
 //config:

modutils/modinfo.c

@@ -8,7 +8,6 @@
 //config:config MODINFO
 //config:	bool "modinfo (24 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	Show information about a Linux Kernel module
 

modutils/modprobe.c

@@ -10,7 +10,6 @@
 //config:config MODPROBE
 //config:	bool "modprobe (28 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	Handle the loading of modules, and their dependencies on a high
 //config:	level.

modutils/rmmod.c

@@ -10,7 +10,6 @@
 //config:config RMMOD
 //config:	bool "rmmod (3.3 kb)"
 //config:	default y
-//config:	select PLATFORM_LINUX
 //config:	help
 //config:	rmmod is used to unload specified modules from the kernel.