build: create two versions of ARM builtins

[compnerd]

Summary

This adds a new name for ARM32 (armhf). We now force that the default build for
ARM32 (arm) to be soft-float ABI. This has a corresponding clang change to look
for these names based on the floating point ABI. The functions are built
identically (the functions are marked as AAPCS, so the calling convention does
not change, as per the RTABI specification), however, the object file contains
attributes indicating the build configuration which the linker will ensure are
not mix and matched. We now built the appropriate named archive so that we can
link properly.

[jroelofs]

LGTM

cmake/config-ix.cmake

     test_target_arch(mips "" "-mips32r2" "--target=mips-linux-gnu")
     test_target_arch(mips64 "" "-mips64r2" "-mabi=n64")
   elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "arm")
-    test_target_arch(arm "" "-march=armv7-a")
+    test_target_arch(arm "" "-march=armv7-a -mfloat-abi=soft")
+    test_target_arch(armhf "" "-march=armv7-a -mfloat-abi=hard")
   elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "aarch32")
     test_target_arch(aarch32 "" "-march=armv8-a")
   elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "aarch64")

 endfunction()
 
 set(ARM64 aarch64)
-set(ARM32 arm)
+set(ARM32 arm armhf)
 set(X86 i386 i686)
 set(X86_64 x86_64)
 set(MIPS32 mips mipsel)

lib/builtins/CMakeLists.txt

   trunctfsf2.c
   ${GENERIC_SOURCES})
 
+set(armhf_SOURCES ${arm_SOURCES})
 set(armv7_SOURCES ${arm_SOURCES})
 set(armv7s_SOURCES ${arm_SOURCES})
 set(arm64_SOURCES ${aarch64_SOURCES})