[compiler-rt][tests] Removed the use of parentheses in compiler-rt tests with lit internal shell (#105729)

This patch addresses compatibility issues with the lit internal shell by
removing the use of subshell execution (parentheses and subshell syntax)
in the `merge-posix.test` and `vptr.cpp` tests. The lit internal shell
does not support parentheses, so the tests have been refactored to use
separate command invocations.

This change is relevant for enabling the lit internal shell by default,
as outlined in [[RFC] Enabling the Lit Internal Shell by
Default](https://discourse.llvm.org/t/rfc-enabling-the-lit-internal-shell-by-default/80179)

fixes: #102401

Author: Harini0924

compiler-rt/test/ubsan/TestCases/TypeCheck/vptr.cpp

@@ -23,7 +23,7 @@
 // RUN: %env_ubsan_opts=halt_on_error=1 not %run %t nN 2>&1 | FileCheck %s --check-prefix=CHECK-NULL-MEMFUN --strict-whitespace
 // RUN: %env_ubsan_opts=print_stacktrace=1 %run %t dT 2>&1 | FileCheck %s --check-prefix=CHECK-DYNAMIC --allow-unused-prefixes --check-prefix=CHECK-%os-DYNAMIC --strict-whitespace
 
-// RUN: (echo "vptr_check:S"; echo "vptr_check:T"; echo "vptr_check:U") > %t.supp
+// RUN: echo -e "vptr_check:S\nvptr_check:T\nvptr_check:U" > %t.supp
 // RUN: %env_ubsan_opts=halt_on_error=1:suppressions='"%t.supp"' %run %t mS
 // RUN: %env_ubsan_opts=halt_on_error=1:suppressions='"%t.supp"' %run %t fS
 // RUN: %env_ubsan_opts=halt_on_error=1:suppressions='"%t.supp"' %run %t cS