configure: common usage

supported switches:
-------------------
	--help

	--nickname
	--program-prefix
	--avoid-version
	--source-dir

	--pkgname
	--pkgdesc
	--pkgusrc
	--pkgrepo
	--pkgpsrc
	--pkgdurl
	--pkgdefs
	--pkglibs

	--prefix
	--exec-prefix
	--bindir
	--sbindir
	--libdir
	--includedir
	--oldincludedir
	--mandir
	--docdir
	--libexecdir

	--sysconfdir
	--sharedstatedir
	--localstatedir
	--runstatedir
	--datarootdir
	--datadir
	--infodir
	--localedir
	--htmldir
	--dvidir
	--pdfdir
	--psdir

	--build
	--host
	--cchost
	--cfghost
	--target
	--arch
	--compiler
	--toolchain
	--sysroot
	--cross-compile
	--shell
	--debug

	--strict
	--ccstrict
	--ldstrict

	--all-static
	--all-shared
	--enable-static
	--enable-shared
	--disable-static
	--disable-shared

	--enable-app
	--enable-frontend
	--disable-app
	--disable-frontend

	--enable-dependency-tracking
	--disable-dependency-tracking


supported variables:
--------------------
	NICKNAME
	SOURCE_DIR

	PREFIX
	EXEC_PREFIX
	BINDIR
	SBINDIR
	LIBDIR
	INCLUDEDIR
	MANDIR
	DOCDIR
	LIBEXECDIR

	SYSCONFDIR
	SHAREDSTATEDIR
	LOCALSTATEDIR
	RUNSTATEDIR
	DATAROOTDIR
	DATADIR
	INFODIR
	LOCALEDIR
	HTMLDIR
	DVIDIR
	PDFDIR
	PSDIR

	CC
	CPP
	CXX

	BUILD
	HOST
	CCHOST
	CFGHOST
	TARGET
	ARCH
	COMPILER
	TOOLCHAIN
	SYSROOT
	CROSS_COMPILE
	SHELL

	CFLAGS
	CFLAGS_DEBUG
	CFLAGS_COMMON
	CFLAGS_CMDLINE
	CFLAGS_CONFIG
	CFLAGS_SYSROOT
	CFLAGS_OS
	CFLAGS_SITE
	CFLAGS_PATH
	CFLAGS_STRICT
	CFLAGS_UTIL
	CFLAGS_LAST
	CFLAGS_ONCE

	LDFLAGS
	LDFLAGS_DEBUG
	LDFLAGS_COMMON
	LDFLAGS_CMDLINE
	LDFLAGS_CONFIG
	LDFLAGS_SYSROOT
	LDFLAGS_PATH
	LDFLAGS_STRICT
	LDFLAGS_UTIL
	LDFLAGS_LAST
	LDFLAGS_ONCE

	PE_SUBSYSTEM
	PE_IMAGE_BASE
	PE_CONFIG_DEFS

	ELF_EH_FRAME
	ELF_HASH_STYLE
	ELF_CONFIG_DEFS

	NATIVE_CC
	NATIVE_CPP
	NATIVE_CXX

	NATIVE_HOST
	NATIVE_CFGHOST
	NATIVE_CFLAGS
	NATIVE_LDFLAGS

	NATIVE_OS
	NATIVE_OS_BITS
	NATIVE_OS_UNDERSCORE