Rebase: [NFC] Refactor sources to be buildable in shared mode

Summary:
Moves source files into separate components, and make explicit
component dependency on each other, so LLVM build system knows how to
build BOLT in BUILD_SHARED_LIBS=ON.

Please use the -c merge.renamelimit=230 git option when rebasing your
work on top of this change.

To achieve this, we create a new library to hold core IR files (most
classes beginning with Binary in their names), a new library to hold
Utils, some command line options shared across both RewriteInstance
and core IR files, a new library called Rewrite to hold most classes
concerned with running top-level functions coordinating the binary
rewriting process, and a new library called Profile to hold classes
dealing with profile reading and writing.

To remove the dependency from BinaryContext into X86-specific classes,
we do some refactoring on the BinaryContext constructor to receive a
reference to the specific backend directly from RewriteInstance. Then,
the dependency on X86 or AArch64-specific classes is transfered to the
Rewrite library. We can't have the Core library depend on targets
because targets depend on Core (which would create a cycle).

Files implementing the entry point of a tool are transferred to the
tools/ folder. All header files are transferred to the include/
folder. The src/ folder was renamed to lib/.

(cherry picked from FBD32746834)

bolt/lib/Utils/CMakeLists.txt

@@ -0,0 +1,53 @@
+# Get the current git revision for BOLT.
+function(get_version ofn)
+  find_program(git_executable NAMES git git.exe git.cmd)
+  if (git_executable)
+    execute_process(COMMAND ${git_executable} rev-parse HEAD
+      WORKING_DIRECTORY ${LLVM_MAIN_SRC_DIR}
+      TIMEOUT 5
+      RESULT_VARIABLE git_result
+      OUTPUT_VARIABLE git_output)
+      if( git_result EQUAL 0 )
+        string(STRIP "${git_output}" git_ref_id)
+        set(BOLT_REVISION "${git_ref_id}")
+      endif()
+  endif()
+
+  # If we can't find a revision, set it to "<unknown>".
+  if (NOT BOLT_REVISION)
+    set(BOLT_REVISION "<unknown>")
+  endif()
+
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+    COMMAND echo '"${BOLT_REVISION}"' > ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+    COMMENT "Generating bogus ${ofn}..."
+  )
+
+  set(VERSION_OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn} PARENT_SCOPE)
+
+  # `make clean' must remove all those generated files:
+  set_property(DIRECTORY APPEND
+    PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${ofn})
+  set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/${ofn} PROPERTIES
+    GENERATED 1)
+endfunction()
+
+# Creates a public target for generating the revision file.
+function(add_public_gen_version_target target)
+  add_custom_target(${target} DEPENDS ${VERSION_OUTPUT})
+  set(LLVM_COMMON_DEPENDS ${LLVM_COMMON_DEPENDS} ${target} PARENT_SCOPE)
+endfunction()
+
+get_version(BoltRevision.inc)
+add_public_gen_version_target(GenBoltRevision)
+
+add_llvm_library(LLVMBOLTUtils
+  CommandLineOpts.cpp
+  Utils.cpp
+
+  LINK_LIBS
+  ${LLVM_PTHREAD_LIB}
+
+  LINK_COMPONENTS
+  Support
+  )