[LLDB] Avoid using -fno-builtin for building API tests

This patch removes use of -fno-builtin flag for building LLDB API
tests.

LLDB API tests are built using Makefile.rules where we were using
-fno-builtin flag to avoid gcc intrinsic optimization conflicting
with Android runtime in past.

Now that we no longer use gcc for building testsuite and compiling
LLDB API tests on AArch64/Windows require clang to optimize certain
calls like _setjmp to setjmpex as former is not implemented by
AArch64 windows runtime.

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

@@ -214,7 +214,7 @@ endif
 
 DEBUG_INFO_FLAG ?= -g
 
-CFLAGS ?= $(DEBUG_INFO_FLAG) -O0 -fno-builtin
+CFLAGS ?= $(DEBUG_INFO_FLAG) -O0
 
 ifeq "$(OS)" "Darwin"
 	ifneq "$(SDKROOT)" ""