avr: add support for AVR 8-bit architecture

This commit adds support for the Atmel AVR 8-bit RISC architecture.
This is the first 8-bit architecture to be added to crosstool-ng so the
configuration options for 8-bit architectures are added here as well.

gcc has had support for AVR for quite a while, at least since the 4.3
series for the currently popular ATmega microcontroler series.
The AVR architecture only supports bare-metal toolchains.

gcc for the AVR 8-bit architecture, usually referred to as avr-gcc, is
commonly used in conjunction with the avr-libc library which provides
additional resources for the Atmel AVR 8-bit microcontrollers.

avr-gcc can also be found as a supported package in some recent Linux
distributions.

This commit also closes #66

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>

config/arch/avr.in

@@ -0,0 +1,8 @@
+# AVR specific config options
+
+## select ARCH_SUPPORTS_8
+## select ARCH_DEFAULT_8
+## select ARCH_REQUIRES_MULTILIB
+##
+## help The 8-bit AVR architecture, as defined by:
+## help     http://www.atmel.com/products/microcontrollers/avr

config/kernel/linux.in

@@ -1,5 +1,6 @@
 # Linux kernel options
 
+## depends on ! ARCH_avr
 ## select KERNEL_SUPPORTS_SHARED_LIBS
 ##
 ## help Build a toolchain targeting systems running Linux as a kernel.

config/target.in

@@ -8,6 +8,7 @@ config ARCH
 # Pre-declare target optimisation variables
 config ARCH_SUPPORTS_BOTH_MMU
 config ARCH_SUPPORTS_BOTH_ENDIAN
+config ARCH_SUPPORTS_8
 config ARCH_SUPPORTS_32
 config ARCH_SUPPORTS_64
 config ARCH_SUPPORTS_WITH_ARCH
@@ -60,6 +61,10 @@ config ARCH_SUFFIX
 comment "Generic target options"
 
 #--------------------------------------
+config ARCH_REQUIRES_MULTILIB
+    bool
+    select MULTILIB
+
 config MULTILIB
     bool
     prompt "Build a multilib toolchain (READ HELP!!!)"
@@ -133,12 +138,18 @@ config ARCH_ENDIAN
     default "little"    if ARCH_LE
 
 #--------------------------------------
+config ARCH_SUPPORTS_8
+    bool
+
 config ARCH_SUPPORTS_32
     bool
 
 config ARCH_SUPPORTS_64
     bool
 
+config ARCH_DEFAULT_8
+    bool
+
 config ARCH_DEFAULT_32
     bool
 
@@ -147,15 +158,22 @@ config ARCH_DEFAULT_64
 
 config ARCH_BITNESS
     int
+    default "8"     if ARCH_8
     default "32"    if ARCH_32
     default "64"    if ARCH_64
 
 choice
     bool
     prompt "Bitness:"
+    default ARCH_8  if ARCH_DEFAULT_8
     default ARCH_32 if ARCH_DEFAULT_32
     default ARCH_64 if ARCH_DEFAULT_64
 
+config ARCH_8
+    bool
+    prompt "8-bit"
+    depends on ARCH_SUPPORTS_8
+
 config ARCH_32
     bool
     prompt "32-bit"

scripts/build/arch/avr.sh

@@ -0,0 +1,5 @@
+# Compute AVR-specific values
+
+CT_DoArchTupleValues() {
+    CT_TARGET_ARCH="${CT_ARCH}"
+}