Revert "[gn build] Add rules for crtbegin/end (#66012)"

This reverts commit e2e32f0.

Breaks bots, e.g. http://45.33.8.238/linux/120748/step_4.txt

llvm/utils/gn/secondary/compiler-rt/lib/BUILD.gn

@@ -5,10 +5,7 @@ group("lib") {
     "//compiler-rt/lib/cfi:ignorelist($host_toolchain)",
   ]
   if (current_os == "linux") {
-    deps += [
-      "//compiler-rt/lib/builtins:crt",
-      "//compiler-rt/lib/msan",
-    ]
+    deps += [ "//compiler-rt/lib/msan" ]
   }
   if (current_os == "linux" || current_os == "android") {
     deps += [ "//compiler-rt/lib/ubsan_minimal" ]

llvm/utils/gn/secondary/compiler-rt/lib/builtins/BUILD.gn

@@ -574,38 +574,6 @@ static_library("builtins") {
   deps = lse_targets
 }
 
-if (current_os == "linux") {
-  source_set("crt_src") {
-    sources = [
-      "crtbegin.c",
-      "crtend.c",
-    ]
-    cflags = [
-      "-std=c11",
-      "-fPIC",
-    ]
-  }
-  copy("crtbegin") {
-    # TODO: use get_target_outputs if it ever works with source_set to avoid hardcoding crt_src.crtbegin.o
-    input_dir = get_label_info(":crt_src", "target_out_dir")
-    sources = [ "$input_dir/crt_src.crtbegin.o" ]
-    outputs = [ "$crt_current_out_dir/clang_rt.crtbegin.o" ]
-    deps = [ ":crt_src" ]
-  }
-  copy("crtend") {
-    input_dir = get_label_info(":crt_src", "target_out_dir")
-    sources = [ "$input_dir/crt_src.crtend.o" ]
-    outputs = [ "$crt_current_out_dir/clang_rt.crtend.o" ]
-    deps = [ ":crt_src" ]
-  }
-  group("crt") {
-    deps = [
-      ":crtbegin",
-      ":crtend",
-    ]
-  }
-}
-
 # Currently unused but necessary to make sync_source_lists_from_cmake.py happy.
 source_set("_unused") {
   sources = [