Enable plan 9 as a valid compiler target

vlib/os/os.v

@@ -415,6 +415,9 @@ pub fn user_os() string {
 	$if serenity {
 		return 'serenity'
 	}
+	//$if plan9 {
+	//	return 'plan9'
+	//}
 	$if vinix {
 		return 'vinix'
 	}

vlib/v/ast/comptime_valid_idents.v

@@ -3,7 +3,7 @@ module ast
 pub const (
 	valid_comptime_if_os             = ['windows', 'ios', 'macos', 'mach', 'darwin', 'hpux', 'gnu',
 		'qnx', 'linux', 'freebsd', 'openbsd', 'netbsd', 'bsd', 'dragonfly', 'android', 'termux',
-		'solaris', 'haiku', 'serenity', 'vinix']
+		'solaris', 'haiku', 'serenity', 'vinix', 'plan9']
 	valid_comptime_if_compilers      = ['gcc', 'tinyc', 'clang', 'mingw', 'msvc', 'cplusplus']
 	valid_comptime_if_platforms      = ['amd64', 'i386', 'aarch64', 'arm64', 'arm32', 'rv64', 'rv32']
 	valid_comptime_if_cpu_features   = ['x64', 'x32', 'little_endian', 'big_endian']

vlib/v/doc/doc.v

@@ -42,6 +42,7 @@ pub enum Platform {
 	termux // like android, but note that termux is running on devices natively, not cross compiling from other platforms
 	solaris
 	serenity
+	plan9
 	vinix
 	haiku
 	raw
@@ -63,6 +64,7 @@ pub fn platform_from_string(platform_str string) !Platform {
 		'js' { return .js }
 		'solaris' { return .solaris }
 		'serenity' { return .serenity }
+		'plan9' {return .plan9}
 		'vinix' { return .vinix }
 		'android' { return .android }
 		'termux' { return .termux }

vlib/v/gen/c/cheaders.v

@@ -328,10 +328,10 @@ const c_common_macros = '
 		#else
 			// On linux: int backtrace(void **__array, int __size);
 			// On BSD: size_t backtrace(void **, size_t);
-		#endif		
+		#endif
 	#endif
 #endif
-		      
+
 #ifdef __TINYC__
 	#define _Atomic volatile
 	#undef EMPTY_STRUCT_DECLARATION
@@ -558,6 +558,11 @@ voidptr memdup(voidptr src, int sz);
 	#include <sys/wait.h> // os__wait uses wait on nix
 #endif
 
+#if defined(__plan9__)
+	#include <u.h>
+	#include <libc.h>
+#endif
+
 #ifdef __OpenBSD__
 	#include <sys/types.h>
 	#include <sys/resource.h>

vlib/v/gen/c/comptime.v

@@ -1042,6 +1042,9 @@ fn (mut g Gen) comptime_if_to_ifdef(name string, is_comptime_option bool) !strin
 		'serenity' {
 			return '__serenity__'
 		}
+		'plan9' {
+			return '__plan9__'
+		}
 		'vinix' {
 			return '__vinix__'
 		}

vlib/v/gen/native/comptime.v

@@ -98,6 +98,9 @@ fn (mut g Gen) comptime_ident(name string, is_comptime_option bool) bool {
 		'serenity' {
 			g.pref.os == .serenity
 		}
+		'plan9' {
+			g.pref.os == .plan9
+		}
 		'vinix' {
 			g.pref.os == .vinix
 		}

vlib/v/help/build/build-c.txt

@@ -125,6 +125,7 @@ see also `v help build`.
             `android`, `termux`,
             `freebsd`, `openbsd`, `netbsd`, `dragonfly`,
             `solaris`, `serenity`, `haiku`,
+            `plan9`,
             `wasm32`, `wasm32-wasi`, `wasm32-emscripten`
 
       Note that V has the concept of platform files, i.e. files ending
@@ -325,4 +326,4 @@ see also `v help build`.
           https://learn.microsoft.com/en-us/cpp/build/reference/fp-specify-floating-point-behavior?view=msvc-170&redirectedfrom=MSDN
           https://clang.llvm.org/docs/UsersManual.html#cmdoption-ffast-math
           https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-ffast-math
-   
+

vlib/v/pref/os.v

@@ -23,6 +23,7 @@ pub enum OS {
 	solaris
 	qnx
 	serenity
+	plan9
 	vinix
 	haiku
 	wasm32
@@ -85,6 +86,9 @@ pub fn os_from_string(os_str string) !OS {
 		'serenity' {
 			return .serenity
 		}
+		'plan9' {
+			return .plan9
+		}
 		'vinix' {
 			return .vinix
 		}
@@ -154,6 +158,7 @@ pub fn (o OS) str() string {
 		.solaris { return 'Solaris' }
 		.qnx { return 'QNX' }
 		.serenity { return 'SerenityOS' }
+		.plan9 { return 'Plan9'}
 		.vinix { return 'Vinix' }
 		.haiku { return 'Haiku' }
 		.wasm32 { return 'WebAssembly' }
@@ -207,6 +212,9 @@ pub fn get_host_os() OS {
 	$if serenity {
 		return .serenity
 	}
+	//$if plan9 {
+	//	return .plan9
+	//}
 	$if vinix {
 		return .vinix
 	}

vlib/v/pref/should_compile.v

@@ -218,6 +218,9 @@ pub fn (prefs &Preferences) should_compile_c(file string) bool {
 	if prefs.os != .serenity && file.ends_with('_serenity.c.v') {
 		return false
 	}
+	if prefs.os != .plan9 && file.ends_with('_plan9.c.v') {
+		return false
+	}
 	if prefs.os != .vinix && file.ends_with('_vinix.c.v') {
 		return false
 	}

vlib/x/x.v

@@ -1,3 +1 @@
 module x
-
-pub const description = 'an empty module, used as a placeholder, for other modules'