move bits/unistd_32.h to bits/asm on all targets

Only Vhex had it at the correct place previously.

CMakeLists.txt

@@ -17,10 +17,12 @@ if(FXLIBC_TARGET STREQUAL vhex-sh)
   add_definitions(-D__SUPPORT_VHEX_KERNEL)
 endif()
 
-if(FXLIB_TARGET STREQUAL vhex-x86)
+if(FXLIBC_TARGET STREQUAL vhex-x86)
   list(APPEND TARGET_FOLDERS vhex-generic x86-generic)
   set(FXLIBC_ARCH x86)
   add_definitions(-D__SUPPORT_VHEX_KERNEL)
+  # TODO: Maybe add -nostdinc (but that removes compiler-provided headers like
+  # <stddef.h>), or use another compiler than the system one?
 endif()
 
 if(FXLIBC_TARGET STREQUAL casiowin-fx)

src/posix/unistd/target/casiowin-fx/close.S

@@ -1,4 +1,4 @@
-#include <bits/unistd_32.h>
+#include <bits/asm/unistd_32.h>
 #include <bits/trapa.h>
 .text
 .global	_close