gnu: avr-toolchain: Replace functions with package variables.

* gnu/packages/avr.scm (avr-gcc-7): Rename to avr-gcc.
(avr-libc): Replace function with variable.
(avr-toolchain): Replace function with variable.

gnu/packages/avr.scm

@@ -42,8 +42,8 @@
     (inherit (cross-binutils "avr"))
     (name "avr-binutils")))
 
-(define-public avr-gcc-7
+(define avr-gcc
-  (let ((xgcc (cross-gcc "avr" #:xgcc gcc-7 #:xbinutils avr-binutils)))
+  (let ((xgcc (cross-gcc "avr" #:xgcc gcc #:xbinutils avr-binutils)))
     (package
       (inherit xgcc)
       (name "avr-gcc")
@@ -95,10 +95,10 @@
               (variable "CROSS_LIBRARY_PATH")
               (files '("avr/lib")))))
       (native-inputs
-       `(("gcc" ,gcc-7)
+       `(("gcc" ,gcc)
          ,@(package-native-inputs xgcc))))))
 
-(define (avr-libc avr-gcc)
+(define avr-libc
   (package
     (name "avr-libc")
     (version "2.0.0")
@@ -123,10 +123,9 @@ for use with GCC on Atmel AVR microcontrollers.")
     (license
      (license:non-copyleft "http://www.nongnu.org/avr-libc/LICENSE.txt"))))
 
-(define (avr-toolchain avr-gcc)
+(define-public avr-toolchain
   ;; avr-libc checks the compiler version and passes "--enable-device-lib" for avr-gcc > 5.1.0.
   ;; It wouldn't install the library for atmega32u4 etc if we didn't use the corret avr-gcc.
-  (let ((avr-libc (avr-libc avr-gcc)))
   (package
     (name "avr-toolchain")
     (version (package-version avr-gcc))
@@ -144,9 +143,7 @@ microcontroller development.  This includes the GCC AVR cross compiler and
 avrdude for firmware flashing.  The supported programming languages are C and
 C++.")
     (home-page (package-home-page avr-libc))
-      (license (package-license avr-gcc)))))
+    (license (package-license avr-gcc))))
-
-(define-public avr-toolchain-7 (avr-toolchain avr-gcc-7))
 
 (define-public microscheme
   (package