Revert "[compiler-rt][ARM] Optimized mulsf3 and divsf3" (#167906)

Reverts #161546

One of the buildbots reported a cmake error I don't understand, and
which I didn't get in my own test builds:
```
CMake Error at /var/lib/buildbot/fuchsia-x86_64-linux/llvm-project/compiler-rt/cmake/Modules/CheckAssemblerFlag.cmake:23 (try_compile):
  COMPILE_DEFINITIONS specified on a srcdir type TRY_COMPILE
```

My best guess is that the thing I did in `CheckAssemblerFlag.cmake` only
works on some versions of cmake. But I don't understand the problem well
enough to fix it quickly, so I'm reverting the whole patch and will
reland it later.

Author: statham-arm

compiler-rt/cmake/Modules/CheckAssemblerFlag.cmake

@@ -60,7 +60,6 @@ endif()
 include(builtin-config-ix)
 include(CMakeDependentOption)
 include(CMakePushCheckState)
-include(CheckAssemblerFlag)
 
 option(COMPILER_RT_BUILTINS_HIDE_SYMBOLS
   "Do not export any symbols from the static library." ON)
@@ -424,40 +423,6 @@ set(arm_or_thumb2_base_SOURCES
   ${GENERIC_SOURCES}
 )
 
-option(COMPILER_RT_ARM_OPTIMIZED_FP
-  "On 32-bit Arm, use optimized assembly implementations of FP arithmetic. Likely to increase code size, but be faster." ON)
-
-if(COMPILER_RT_ARM_OPTIMIZED_FP AND BUILTIN_SUPPORTED_ARCH MATCHES "arm")
-  check_assembler_flag(COMPILER_RT_HAS_MIMPLICIT_IT -mimplicit-it=always)
-  if(COMPILER_RT_HAS_MIMPLICIT_IT)
-    set(implicit_it_flag -mimplicit-it=always)
-  else()
-    check_assembler_flag(
-      COMPILER_RT_HAS_WA_MIMPLICIT_IT -Wa,-mimplicit-it=always)
-    if(COMPILER_RT_HAS_WA_MIMPLICIT_IT)
-      set(implicit_it_flag -Wa,-mimplicit-it=always)
-    else()
-      message(WARNING "Don't know how to set the -mimplicit-it=always flag in this assembler; not including Arm optimized implementations")
-      set(implicit_it_flag "")
-    endif()
-  endif()
-
-  if(implicit_it_flag)
-    set(assembly_files
-      arm/mulsf3.S
-      arm/divsf3.S)
-    set_source_files_properties(${assembly_files}
-      PROPERTIES COMPILE_OPTIONS ${implicit_it_flag})
-    set(arm_or_thumb2_base_SOURCES
-      ${assembly_files}
-      arm/fnan2.c
-      arm/fnorm2.c
-      arm/funder.c
-      ${arm_or_thumb2_base_SOURCES}
-      )
-  endif()
-endif()
-
 set(arm_sync_SOURCES
   arm/sync_fetch_and_add_4.S
   arm/sync_fetch_and_add_8.S
@@ -491,16 +456,6 @@ set(thumb1_base_SOURCES
   ${GENERIC_SOURCES}
 )
 
-if(COMPILER_RT_ARM_OPTIMIZED_FP)
-  set(thumb1_base_SOURCES
-    arm/thumb1/mulsf3.S
-    arm/fnan2.c
-    arm/fnorm2.c
-    arm/funder.c
-    ${thumb1_base_SOURCES}
-  )
-endif()
-
 set(arm_EABI_RT_SOURCES
   arm/aeabi_cdcmp.S
   arm/aeabi_cdcmpeq_check_nan.c