all: copy cmd/ld/textflag.h into pkg/GOOS_GOARCH
The file is used by assembly code to define symbols like NOSPLIT.
Having it hidden inside the cmd directory makes it hard to access
outside the standard repository.
Solution: As with a couple of other files used by cgo, copy the
file into the pkg directory and add a -I argument to the assembler
to access it. Thus one can write just
        #include "textflag.h"
in .s files.

The names in runtime are not updated because in the boot sequence the
file has not been copied yet when runtime is built. All other .s files
in the repository are updated.

Changes to doc/asm.html, src/cmd/dist/build.c, and src/cmd/go/build.go
are hand-made. The rest are just the renaming done by a global
substitution. (Yay sam).

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/128050043
diff --git a/doc/asm.html b/doc/asm.html
index f4ef1e6..9433472 100644
--- a/doc/asm.html
+++ b/doc/asm.html
@@ -253,7 +253,7 @@
 If there are two, the first is a bit mask of flags,
 which can be written as numeric expressions, added or or-ed together,
 or can be set symbolically for easier absorption by a human.
-Their values, defined in the file <code>src/cmd/ld/textflag.h</code>, are:
+Their values, defined in the standard <code>#include</code>  file <code>textflag.h</code>, are:
 </p>
 
 <ul>