tc_build: llvm: Ensure LLVM_LINK_LLVM_DYLIB remains off

Currently, this is disabled by default but LLVM upstream is talking
about flipping this value to ON for certain platform. It hurts the speed
of the compiler, which is one of tc-build's primary focuses with the
easy integration of PGO, BOLT, and LTO. Keep this option off to maintain
the status quo.

Link: https://discourse.llvm.org/t/rfc-llvm-link-llvm-dylib-should-default-to-on-on-posix-platforms/85908
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

tc_build/llvm.py

@@ -35,6 +35,10 @@ def __init__(self):
         self.cmake_defines = {
             # Reduce dynamic dependencies
             'LLVM_ENABLE_LIBXML2': 'OFF',
+            # While this option reduces build resources and disk space, it
+            # increases start up time for the tools dynamically linked against
+            # it and limits optimization opportunities for LTO, PGO, and BOLT.
+            'LLVM_LINK_LLVM_DYLIB': 'OFF',
         }
         self.install_targets = []
         self.llvm_major_version = 0