Fix symbol visiblility for compiler-rt builtins on MacOS

The symbols in the compiler-rt builtins library are private external by
default on MacOS. We need them to be visible so we can link against them
(e.g. when building libllvmlite.so). This patch makes the symbols
visible when the CMake option `COMPILER_RT_BUILTINS_HIDE_SYMBOLS` is
off. Note that this is an existing option for the compiler-rt build, and
the flags requiring modification in this patch appear to be an
oversight.

References:

- https://discourse.llvm.org/t/lld-automatically-hide-symbols-with-prefix/73192
- numba#986 (comment)

Author: gmarkall

conda-recipes/compiler-rt-macos-build.patch

@@ -0,0 +1,15 @@
+diff --git a/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake b/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
+index 640c7e7124c9..7bd3edb86eb1 100644
+--- a/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
++++ b/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
+@@ -399,7 +399,9 @@ endfunction()
+ macro(darwin_add_builtin_libraries)
+   set(DARWIN_EXCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/Darwin-excludes)
+ 
+-  set(CFLAGS -fPIC -O3 -fvisibility=hidden -DVISIBILITY_HIDDEN -Wall -fomit-frame-pointer)
++  set(CFLAGS -fPIC -O3 -Wall -fomit-frame-pointer)
++  append_list_if(COMPILER_RT_BUILTINS_HIDE_SYMBOLS -fvisibility=hidden CFLAGS)
++  append_list_if(COMPILER_RT_BUILTINS_HIDE_SYMBOLS -DVISIBILITY_HIDDEN CFLAGS)
+   set(CMAKE_C_FLAGS "")
+   set(CMAKE_CXX_FLAGS "")
+   set(CMAKE_ASM_FLAGS "")

conda-recipes/llvmdev_llvm15/meta.yaml

@@ -1,7 +1,7 @@
 {% set shortversion = "15.0" %}
 {% set version = "15.0.7" %}
 {% set sha256_llvm = "8b5fcb24b4128cf04df1b0b9410ce8b1a729cb3c544e6da885d234280dedeac6" %}
-{% set build_number = "0" %}
+{% set build_number = "1" %}
 
 package:
   name: llvmdev
@@ -15,6 +15,7 @@ source:
     - ../llvm15-remove-use-of-clonefile.patch
     - ../llvm15-svml.patch
     - ../compiler-rt-cfi-startproc-war.patch
+    - ../compiler-rt-macos-build.patch
 
     # Patches from conda-forge needed for windows to build
     # backport of zlib patches, can be dropped for vs15.0.3, see