Revert "wrapper scripts: set (mostly) correct $0"

This reverts commit 06848ee.

Turns out that this breaks e.g. gcc finding its installation path.

% gcc foo.c
gcc: error trying to exec 'cc1': execvp: No such file or directory

% gcc --print-search-dirs
install: /ro/gcc-8.2.0/bin/../lib/gcc/x86_64-pc-linux-gnu/8.2.0/
[…]

% ls /ro/gcc-8.2.0/bin/../lib/gcc/x86_64-pc-linux-gnu/8.2.0/
ls: cannot access '/ro/gcc-8.2.0/bin/../lib/gcc/x86_64-pc-linux-gnu/8.2.0/': No such file or directory

cmd/distri/build.go

@@ -159,9 +159,6 @@ func buildpkg(hermetic, debug, fuse bool) error {
 	return nil
 }
 
-// We need to strip the path from $0 because shebang evaluation doesn’t pass the
-// invoker as $0, but passes the path to the shell script instead.
-// See also https://www.in-ulm.de/~mascheck/various/shebang/
 var wrapperTmpl = template.Must(template.New("").Funcs(template.FuncMap{
 	"quoteenv": func(env string) string {
 		return strings.Replace(env, `=`, `="`, 1) + `"`
@@ -170,7 +167,7 @@ var wrapperTmpl = template.Must(template.New("").Funcs(template.FuncMap{
 {{ range $idx, $env := .Env }}
 export {{ quoteenv $env }}
 {{ end }}
-exec -a "${0##*/}" {{ .Prefix }}/{{ .Bin }} "$@"
+exec {{ .Prefix }}/{{ .Bin }} "$@"
 `))
 
 func (b *buildctx) serialize() (string, error) {