change(build): mild improvements

I'm really regretting writing my own configure script. Some lessons you need to learn the hard way...

configure

@@ -1,7 +1,8 @@
 #!/bin/sh
 
 # A handwritten ./configure script, because I kind of hate autotools.
-# © 2020 Eddie Antonio Santos <[email protected]>
+# Update (2023): Autotools=still awful. But writing this was a mistake.
+# © 2020–2023 Eddie Antonio Santos <[email protected]>
 
 set -e
 
@@ -129,7 +130,7 @@ require_system_header() {
 
 use_cxxflag() {
  flag="$1"
- printf "checking to compile C++ with ${flag}... "
+ printf 'checking to compile C++ with %s...' "${flag}"
 
  compile_test_cxx_program "${flag}" <<EOF
 int main(void) {
@@ -148,11 +149,11 @@ link_lib_against_test_program() {
 
  printf 'checking to link with lib%s [using %s()]... ' "$lib" "$funcname"
  compile_test_program -l"${lib}" <<EOF
- char ${funcname}(void);
+char ${funcname}(void);
 
- int main(void) {
-  return ${funcname}();
- }
+int main(void) {
+ return ${funcname}();
+}
 EOF
 }
 
@@ -164,21 +165,25 @@ link_lib_against_test_program_using_pkgconfig() {
  lib=$2
 
  printf 'checking to link with lib%s using pkg-config [using %s()]... ' "$lib" "$funcname"
- compile_test_program $(pkg-config --cflags --libs lib${lib}) <<EOF
- char ${funcname}(void);
+ # Contrary to best practices, pkg-config actually depends on its output
+ # being broken by spaces to create multiple arguments from one invocation,
+ # so ignore the lint:
+ # shellcheck disable=SC2046
+ compile_test_program $(pkg-config --cflags --libs "lib${lib}") <<EOF
+char ${funcname}(void);
 
- int main(void) {
-  return ${funcname}();
- }
+int main(void) {
+ return ${funcname}();
+}
 EOF
 }
 
 # Add the appropriate flags for the given library using pkg-config(1)
 extend_libs_and_includes_using_pkgconfig() {
  lib=$1
 
- libs="${libs} $(pkg-config --libs lib${lib})"
- includes="${includes} $(pkg-config --cflags lib${lib})"
+ libs="${libs} $(pkg-config --libs "lib${lib}")"
+ includes="${includes} $(pkg-config --cflags "lib${lib}")"
 }
 
 # Check if the program is on the path.
@@ -217,11 +222,11 @@ compile_with_header() {
  # term.h on newer macOS.
  # See: https:/eddieantonio/imgcat/issues/51
  compile_test_program -c <<EOF
- #ifdef __APPLE__
- #include <Availability.h>
- #endif
+#ifdef __APPLE__
+#include <Availability.h>
+#endif
 
- #include <${header}>
+#include <${header}>
 EOF
 }