selfhost: migrate tool sources to directory packages

Build w6a and w6l from package-main directories and expose the wcc backend through a narrow package API so w6c and wwdump no longer import implementation files. Retarget the remaining load-bearing fixtures and example sources to directory packages; retain the one intentional flat compiler collision as an explicitly composed raw unit.

selfhost/cmd/w6l/dyn.ww

@@ -4,12 +4,11 @@
 // exports and which DT_NEEDED entry to record. We do not pull bytes
 // from the .so; the dynamic loader maps it at runtime.
 
-package w6l;
+package main;
 
 import os;
 import rt;
 import strings;
-import sym;
 
 def ET_DYN_SO:     u16 = 3u16;
 def EM_X86_64_SO:  u16 = 62u16;

selfhost/cmd/w6l/dynout.ww

@@ -22,12 +22,11 @@
 //   [gotplt_off]   .got.plt   (writable; mapped by PT_LOAD #2)
 //   [dynamic_off]  .dynamic   (writable; covered by PT_DYNAMIC)
 
-package w6l;
+package main;
 
 import os;
 import rt;
 import strings;
-import sym;
 
 def ET_EXEC_D:     u16 = 2u16;
 def EM_X86_64_D:   u16 = 62u16;

selfhost/cmd/w6l/main.ww

@@ -7,11 +7,6 @@ package main;
 import os;
 import rt;
 import strings;
-import sym;
-import obj;
-import dyn;
-import pass;
-import out;
 
 def BASE: u64 = 4194304u64;	// 0x400000
 def CODE_VA_OFF: u64 = 4096u64;	// .text starts at base + 0x1000

selfhost/cmd/w6l/obj.ww

@@ -1,11 +1,10 @@
 // Port of cmd/w6l/obj.c.
 
-package w6l;
+package main;
 
 import os;
 import rt;
 import strings;
-import sym;
 
 def ET_REL:        i32 = 1;
 def EM_X86_64:     i32 = 62;

selfhost/cmd/w6l/out.ww

@@ -1,11 +1,9 @@
 // Port of cmd/w6l/out.c.
 
-package w6l;
+package main;
 
 import os;
 import rt;
-import sym;
-import dynout;
 
 def ET_EXEC:    u16 = 2u16;
 def EM_X86_64_W: u16 = 62u16;

selfhost/cmd/w6l/pass.ww

@@ -3,11 +3,9 @@
 // Supported relocation kinds: PC32 (=2), PLT32 (=4); both are 32-bit
 // PC-relative displacements (PLT32 == PC32 for static).
 
-package w6l;
+package main;
 
 import os;
-import sym;
-import dyn;
 
 def R_X86_64_64:    i32 = 1;
 def R_X86_64_PC32:  i32 = 2;

selfhost/cmd/w6l/sym.ww

@@ -3,7 +3,7 @@
 // Singly-linked list, usually a few hundred entries; hashing isn't
 // worth it yet.
 
-package w6l;
+package main;
 
 import strings;