config.mk: do not explicitly set CC (#455)

1. `c99` doesn't exist on openbsd
2. `c99` behaves weirdly on macos (doesn't support -Wall)

since make will already set CC (required by POSIX if the implementation
supports C, see `man 1p make`) to something appropriate (or it might be
set in the environment) go ahead and remove explicitly setting it on our
end.

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/455
Reviewed-by: TAAPArthur <taaparthur@noreply.codeberg.org>

.github/workflows/build.yml

@@ -47,7 +47,7 @@ jobs:
       - name: build
         run: |
           # libinotify-kqueue isn't available on homebrew
-          make clean && make -s CC=gcc OPT_DEP_DEFAULT=1 HAVE_INOTIFY=0
+          make clean && make -s OPT_DEP_DEFAULT=1 HAVE_INOTIFY=0
           # force uninstallation with --ignore-dependencies
           brew uninstall --ignore-dependencies libxft libexif giflib webp
-          make clean && make -s CC=gcc OPT_DEP_DEFAULT=0
+          make clean && make -s OPT_DEP_DEFAULT=0

config.mk

@@ -21,8 +21,6 @@ HAVE_LIBEXIF  = $(OPT_DEP_DEFAULT)
 HAVE_LIBGIF   = $(OPT_DEP_DEFAULT)
 HAVE_LIBWEBP  = $(OPT_DEP_DEFAULT)
 
-# Compiler and linker
-CC = c99
 # CFLAGS, any additional compiler flags goes here
 CFLAGS = -Wall -pedantic -O2 -DNDEBUG
 # Uncomment for a debug build using gcc/clang