testdata: remove some unnecessary execs (#267)

Our use of go-internal's gotooltest.Setup means that "go" is set up as a
top-level command in the scripts, so we can simply "go build" instead of
having to "exec go build". The result is practically the same, but the
scripts are simpler.

While at it, I had left an "exec cat" behind; remove it.

testdata/scripts/basic.txt

@@ -28,7 +28,7 @@ stdout 'unknown'
 [short] stop # checking that the build is reproducible is slow
 
 # Check that we fail if the user used "go build -toolexec garble" instead of "garble build"
-! exec go build -a -toolexec=garble main.go
+! go build -a -toolexec=garble main.go
 stderr 'not running "garble \[command\]"'
 
 # Also check that the binary is reproducible.
@@ -41,7 +41,7 @@ bincmp main$exe main_old$exe
 
 # Check that the program works as expected without garble. No need to verify
 # this when we run with -short.
-exec go build main.go
+go build main.go
 exec ./main
 cmp stderr main.stderr
 

testdata/scripts/ldflags.txt

@@ -15,7 +15,7 @@ exec ./main
 cmp stderr main.stderr
 ! binsubstr main$exe 'unexportedVersion'
 
-exec go build -ldflags=${LDFLAGS}
+go build -ldflags=${LDFLAGS}
 exec ./main
 cmp stderr main.stderr
 binsubstr main$exe 'unexportedVersion'

testdata/scripts/modinfo.txt

@@ -7,7 +7,7 @@ cmp stderr main.stderr
 
 [short] stop # no need to verify this with -short
 
-exec go build
+go build
 exec ./main
 cmp stderr main.stderr-orig
 binsubstr main$exe '(devel)'

testdata/scripts/reverse.txt

@@ -8,7 +8,6 @@ env GOPRIVATE=test/main
 garble build
 exec ./main
 cp stderr main.stderr
-exec cat main.stderr
 
 # Ensure that the garbled panic output looks correct.
 # This output is not reproducible between 'go test' runs,

testdata/scripts/test.txt

@@ -16,7 +16,7 @@ stdout 'PASS.*TestSeparateFoo'
 [short] stop # no need to verify this with -short
 
 # verify with regular cmd/go
-exec go test -v
+go test -v
 stdout 'PASS.*TestFoo'
 
 -- go.mod --