Remove CC autodetection from Makefile.rules

[aprantl]

Summary

Auto-detecting CC in Makefile.rules is no longer useful. Every since out-of-tree builds you are better off just running lldb-dotest which sets it directly. This also makes it harder to accidentally unset CC in a Makefile.

[labath]

Yay

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

 # If you change the defaults of CC, be sure to also change it in the file
 # test/plugins/builder_base.py, which provides a Python way to return the
 # value of the make variable CC -- getCompiler().
 #
 # See also these functions:
 #   o cxx_compiler
 #   o cxx_linker
 #----------------------------------------------------------------------
-CC ?= clang
-ifeq "$(CC)" "cc"
-  ifneq "$(shell which clang)" ""
-    CC = clang
-  else ifneq "$(shell which clang-3.5)" ""
-    CC = clang-3.5
-  else ifneq "$(shell which gcc)" ""
-    CC = gcc
-  endif
+ifeq "$(CC)" ""
+$(error "C compiler is not specified. Please run tests through lldb-dotest or lit")
 endif
 
 #----------------------------------------------------------------------
 # Handle SDKROOT on Darwin
 #----------------------------------------------------------------------
 
 ifeq "$(OS)" "Darwin"
     ifeq "$(SDKROOT)" ""