trace: support BSD version of sed in gen.bash

The GNU version of sed (common on Linux) will modify files in place when
it sees the -i flag with no argument at all, as in [sed -i -e '...'].
The BSD version of sed (common on macOS) will modify files in place when
it's given an explicit zero-length argument, as in [sed -i '' -e '...'].

But they agree on at least one way of specifying a non-zero-length
backup suffix, [sed -i '.tmp' -e '...']. Use that and then delete the
backups.

In addition, change the expressions we pass to sed to make them a bit
more explicit and to require less escaping.

Fixes golang/go#68403

Change-Id: Icfc3863f4abe26bc77d9c0bc3b778067db6387de
Reviewed-on: https://go-review.googlesource.com/c/exp/+/598016
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>

trace/gen.bash

@@ -74,21 +74,26 @@ mv $DST/testtrace $DST/internal/testtrace
 mv $DST/testdata/cmd $DST/cmd
 
 # Fix up import paths.
-find $DST -name '*.go' | xargs -- sed -i 's/internal\/trace/golang.org\/x\/exp\/trace/'
-find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/raw/golang.org\/x\/exp\/trace\/internal\/raw/'
-find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/event/golang.org\/x\/exp\/trace\/internal\/event/'
-find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/event\/go122/golang.org\/x\/exp\/trace\/internal\/event\/go122/'
-find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/version/golang.org\/x\/exp\/trace\/internal\/version/'
-find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/testtrace/golang.org\/x\/exp\/trace\/internal\/testtrace/'
-find $DST -name '*.go' | xargs -- sed -i 's/internal\/txtar/golang.org\/x\/tools\/txtar/'
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's internal/trace golang.org/x/exp/trace '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's golang.org/x/exp/trace/raw golang.org/x/exp/trace/internal/raw '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's golang.org/x/exp/trace/event golang.org/x/exp/trace/internal/event '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's golang.org/x/exp/trace/event/go122 golang.org/x/exp/trace/internal/event/go122 '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's golang.org/x/exp/trace/version golang.org/x/exp/trace/internal/version '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's golang.org/x/exp/trace/testtrace golang.org/x/exp/trace/internal/testtrace '
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e 's internal/txtar golang.org/x/tools/txtar '
 
 # Add build tag for Go 1.21 and generated code comment.
-find $DST -name '*.go' | xargs -- sed -i '/LICENSE file./a \
+find $DST -name '*.go' | xargs -- sed -i'.tmp' -e '/LICENSE file./a \
 \
-// Code generated by "gen.bash" from internal/trace; DO NOT EDIT.\n\n//go:build go1.21'
+// Code generated by "gen.bash" from internal/trace; DO NOT EDIT.\
+\
+//go:build go1.21'
 
 # Format the files.
 find $DST -name '*.go' | xargs -- gofmt -w -s
 
+# Delete sed backups
+find $DST -name '*.go.tmp' -delete
+
 # Restore known files.
 git checkout gen.bash flightrecorder.go flightrecorder_test.go