ANDROID: build.config.common: enable LLVM=1

This moves builds to all use LLVM=1 argument to make, rather than
CC=clang NM=llvm-nm OBJCOPY=llvm-objcopy ... (see also
https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities).

Step 3 of aosp/1405387.

Bug: 65987925
Bug: 141693040
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: I0975dcad48b6c5344124343606e1c7f85e76e4ee
diff --git a/build.config.common b/build.config.common
index a465422..a1ea332 100644
--- a/build.config.common
+++ b/build.config.common
@@ -1,10 +1,7 @@
 BRANCH=android-mainline
 KMI_GENERATION=0
 
-CC=clang
-LD=ld.lld
-NM=llvm-nm
-OBJCOPY=llvm-objcopy
+LLVM=1
 DEPMOD=depmod
 DTC=dtc
 CLANG_PREBUILT_BIN=prebuilts-master/clang/host/linux-x86/clang-r383902/bin