Avoid sub shell

[rnk]

lgtm

I was thinking that the alternative fix would be to add a flag to not like not --dont-care diff a.txt b.txt | grep "^<", but this works.

compiler-rt/test/asan/TestCases/Linux/coverage-missing.cc

 // RUN: %sancov print *.sancov > bar.txt
 // RUN: rm *.sancov
 // RUN: count 4 < bar.txt
 // RUN: %sancov missing %t < foo.txt > foo-missing.txt
 // RUN: sort main.txt foo-missing.txt -o foo-missing-with-main.txt
 // The "missing from foo" set may contain a few bogus PCs from the sanitizer
 // runtime, but it must include the entire "bar" code path as a subset. Sorted
 // lists can be tested for set inclusion with diff + grep.
-// RUN: ( diff bar.txt foo-missing-with-main.txt || true ) | not grep "^<"
+// RUN: diff bar.txt foo-missing-with-main.txt > %t.log || true
+// RUN: not grep "^<" %t.log
 
 // Second case: coverage from DSO.
 // cd %T
 // RUN: %clangxx_asan -fsanitize-coverage=func %s -o %dynamiclib -DFOOBAR -shared -fPIC
 // RUN: %clangxx_asan -fsanitize-coverage=func %s %dynamiclib -o %t -DMAIN
 // RUN: export LIBNAME=`basename %dynamiclib`
 // RUN: rm -rf %T/coverage-missing
 // RUN: mkdir -p %T/coverage-missing
 // RUN: cd %T/coverage-missing
 // RUN: %env_asan_opts=coverage=1:coverage_dir=%T/coverage-missing %run %t x
 // RUN: %sancov print $LIBNAME.*.sancov > foo.txt
 // RUN: rm *.sancov
 // RUN: count 2 < foo.txt
 // RUN: %env_asan_opts=coverage=1:coverage_dir=%T/coverage-missing %run %t x x
 // RUN: %sancov print $LIBNAME.*.sancov > bar.txt
 // RUN: rm *.sancov
 // RUN: count 3 < bar.txt
 // RUN: %sancov missing %dynamiclib < foo.txt > foo-missing.txt
-// RUN: ( diff bar.txt foo-missing.txt || true ) | not grep "^<"
+// RUN: diff bar.txt foo-missing.txt > %t.log || true
+// RUN: not grep "^<" %t.log
 
 // REQUIRES: x86-target-arch
 // XFAIL: android
 
 #include <stdio.h>
 
 void foo1();
 void foo2();