R-scripts nuked by osx-arm migrator

[h-vetinari]

The bot added the following diff in conda-forge/r-arrow-feedstock#88:

--- a/recipe/build.sh
+++ b/recipe/build.sh
@@ -1,16 +1,6 @@
 #!/bin/bash
-set -ex

 export DISABLE_AUTOBREW=1

-# arrow uses C++17
-export ARROW_R_CXXFLAGS="${ARROW_R_CXXFLAGS} -std=c++17"
-export LIBARROW_BUILD=false
-
-if [[ "${target_platform}" == osx-* ]]; then
-    # See https://conda-forge.org/docs/maintainer/knowledge_base.html#newer-c-features-with-old-sdk
-    export ARROW_R_CXXFLAGS="${ARROW_R_CXXFLAGS} -D_LIBCPP_DISABLE_AVAILABILITY"
-fi
-
-# ${R_ARGS} necessary to support cross-compilation
-${R} CMD INSTALL --build r/. ${R_ARGS}
+# shellcheck disable=SC2086
+${R} CMD INSTALL --build . ${R_ARGS}

which looks like it's blindly (and incorrectly) overwriting the build script - @beckermr asked me to open an issue here.

I've looked at https://github.com/regro/cf-scripts/blob/master/conda_forge_tick/migrators/arch.py, but cannot figure out why the osx-arm migrator would do that. Also of note, the linux-arches PR for the same branch did not cause such changes to the build script.

[beckermr]

I expect this may be a minimigrator and not the primary one.

[h-vetinari]

I expect this may be a minimigrator and not the primary one.

Yeah, but I couldn't find which one would do that. At least, none of the names in https://github.com/regro/cf-scripts/blob/master/conda_forge_tick/migrators stick out.

[beckermr]

This happens here: https://github.com/regro/cf-scripts/blob/master/conda_forge_tick/migrators/cross_compile.py#L365.

cc @isuruf for advice on how to proceed.

[beckermr]

Likely related to the comment @isuruf made here: #2946 (comment)