[Obvious] Change Linux to GNU/LINUX in ARM options documentation

gcc/
	* doc/invoke.texi (-march): Use GNU/Linux rather than Linux.
	(-mtune): Likewise.
	(-mcpu): Likewise.

From-SVN: r215049

gcc/ChangeLog

+2014-09-09  James Greenhalgh  <james.greenhalgh@arm.com>
+
+	* doc/invoke.texi (-march): Use GNU/Linux rather than Linux.
+	(-mtune): Likewise.
+	(-mcpu): Likewise.
+
 2014-09-09  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/61749

gcc/doc/invoke.texi

@@ -12567,8 +12567,8 @@ architecture together with the optional CRC32 extensions.
 
 @option{-march=native} causes the compiler to auto-detect the architecture
 of the build computer.  At present, this feature is only supported on
-Linux, and not all architectures are recognized.  If the auto-detect is
-unsuccessful the option has no effect.
+GNU/Linux, and not all architectures are recognized.  If the auto-detect
+is unsuccessful the option has no effect.
 
 @item -mtune=@var{name}
 @opindex mtune
@@ -12619,7 +12619,7 @@ this option may change in future GCC versions as CPU models come and go.
 
 @option{-mtune=native} causes the compiler to auto-detect the CPU
 of the build computer.  At present, this feature is only supported on
-Linux, and not all architectures are recognized.  If the auto-detect is
+GNU/Linux, and not all architectures are recognized.  If the auto-detect is
 unsuccessful the option has no effect.
 
 @item -mcpu=@var{name}
@@ -12640,8 +12640,8 @@ See @option{-mtune} for more information.
 
 @option{-mcpu=native} causes the compiler to auto-detect the CPU
 of the build computer.  At present, this feature is only supported on
-Linux, and not all architectures are recognized.  If the auto-detect is
-unsuccessful the option has no effect.
+GNU/Linux, and not all architectures are recognized.  If the auto-detect
+is unsuccessful the option has no effect.
 
 @item -mfpu=@var{name}
 @opindex mfpu