blacklist GNU as keyword

fixes #23

Author: pboettch

extract-upper-case.pl

@@ -19,7 +19,7 @@
 my @languages = qw(ASM ASM_MASM ASM_NASM C CSharp CUDA CXX Fortran Java RC Swift);
 
 # unwanted upper-cases
-my %unwanted = map { $_ => 1 } qw(VS CXX IDE NOTFOUND NO_ DFOO DBAR NEW);
+my %unwanted = map { $_ => 1 } qw(VS CXX IDE NOTFOUND NO_ DFOO DBAR NEW GNU);
 	# cannot remove ALL - exists for add_custom_command
 
 # control-statements

syntax/cmake.vim

@@ -2481,7 +2481,6 @@ syn keyword cmakeKWadd_link_options contained
             \ CUDA_SEPARABLE_COMPILATION
             \ DEVICE_LINK
             \ GCC
-            \ GNU
             \ HOST_LINK
             \ LANG
             \ LINKER
@@ -4076,7 +4075,6 @@ syn keyword cmakeKWtarget_link_options contained
             \ CUDA_SEPARABLE_COMPILATION
             \ DEVICE_LINK
             \ GCC
-            \ GNU
             \ HOST_LINK
             \ IMPORTED
             \ INTERFACE
@@ -4334,7 +4332,6 @@ syn keyword cmakeGeneratorExpressions contained
             \ GET_ROOT_NAME
             \ GET_ROOT_PATH
             \ GET_STEM
-            \ GNU
             \ HAS_
             \ HAS_EXTENSION
             \ HAS_FILENAME