lib/R/etc/Makeconf missing C compiler entries

[mfansler]

The lib/R/etc/Makeconf files in linux-aarch64, linux-ppc64le, and osx-arm64 are missing entries for C compilers, e.g.:

osx-arm64

## C compilers
CC = arm64-apple-darwin20.0.0-clang
CFLAGS =  -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/jqm406/miniforge3/envs/r44/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1719893340331/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/jqm406/miniforge3/envs/r44=/usr/local/src/conda-prefix $(LTO)
CC17 = 
C17FLAGS =  $(LTO)
CC23 = 
C23FLAGS =  $(LTO)
CC90 = 
C90FLAGS =  $(LTO)
CC99 = 
C99FLAGS =  $(LTO)
CPICFLAGS = -fPIC
CPPFLAGS =  -D_FORTIFY_SOURCE=2 -isystem /Users/jqm406/miniforge3/envs/r44/include -mmacosx-version-min=11.0 -mmacosx-version-min=11.0 -I/Users/jqm406/miniforge3/envs/r44/include
C_VISIBILITY = 

osx-64 (Good)

## C compilers
CC = x86_64-apple-darwin13.4.0-clang
CFLAGS =  -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh=/usr/local/src/conda-prefix $(LTO)
CC17 = x86_64-apple-darwin13.4.0-clang -std=gnu17
C17FLAGS =  -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh=/usr/local/src/conda-prefix $(LTO)
CC23 = x86_64-apple-darwin13.4.0-clang -std=gnu2x
C23FLAGS =  -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh=/usr/local/src/conda-prefix $(LTO)
CC90 = x86_64-apple-darwin13.4.0-clang -std=gnu90
C90FLAGS =  -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh=/usr/local/src/conda-prefix $(LTO)
CC99 = x86_64-apple-darwin13.4.0-clang -std=gnu99
C99FLAGS =  -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/work=/usr/local/src/conda/r-base-4.4.1 -fdebug-prefix-map=/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh=/usr/local/src/conda-prefix $(LTO)
CPICFLAGS = -fPIC
CPPFLAGS =  -D_FORTIFY_SOURCE=2 -isystem /Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include -mmacosx-version-min=10.13 -mmacosx-version-min=10.13 -I/Users/runner/miniforge3/conda-bld/r-base-split_1723488738748/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/include
C_VISIBILITY = 

This is driving errors on these platforms whenever R packages depend on these environment variables during installation (e.g., conda-forge/r-locfit-feedstock#20).