recipe/build.sh: incredible hacks to build on macOS

Ran into a whole pile of exciting problems. Analysis and workarounds
documented extensively in the build scripts.

recipe/build.sh

@@ -10,13 +10,47 @@ if [ $(uname) = Darwin ] ; then
     export CXXFLAGS="-arch $OSX_ARCH -stdlib=libc++ -std=c++11"
     export RUSTFLAGS="-C link-args=-Wl,-rpath,$PREFIX/lib"
 
-    # Well, I have no idea what's going on here. But if we don't run these
-    # programs like this, the build fails with errors about not being able to
-    # find "cc" and "ar". ???? -- PKGW 2018 Sep 16.
+    # HACK: Well, I have no idea what's going on here. But if we don't run
+    # these programs like this, the build fails with errors about not being
+    # able to find the various developer tools:
+    #
+    # /Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild -sdk / -find clang 2> /dev/null
+    # cc: error: unable to find utility "clang", not a developer tool or in PATH
+    #
+    # Certain dependent libraries compile C code in ways that don't respect
+    # $CC, so to cover all the bases for all toolchains we need to invoke `cc`
+    # explicitly.
     set +e
     cc --help
+    $CC --help
+    $CXX --help
     ar --help
     set -e
+
+    # HACK: work around https://github.com/rust-lang/rust/issues/51838 .
+    # On Travis we currently use an old version of macOS that crashes
+    # when rustc tries to resize the stack of its main thread. By setting
+    # hard stack size ulimit to be smaller than Rust wants, we trigger code
+    # in rustc that launches the compiler in a thread, avoiding the crash.
+    ulimit -s 1024
+
+    # HACK: work around
+    # https://github.com/rust-lang/cargo/issues/2888#issuecomment-431049264 .
+    # To configure the build Cargo compiles and executes the Tectonic "build
+    # script", which in turn invokes pkg-config. But cargo runs the build
+    # script with DYLD_LIBRARY_PATH set, which causes pkg-config to fail: the
+    # environment variable causes the linker to try to link the system's
+    # libcups with conda-forge's libiconv, which is incompatible with the
+    # system version. As it happens, conda-forge's pkg-config is already a
+    # wrapper script, so we hack it to unset the variable. Fun times.
+    pc=$(which pkg-config)
+    cp $pc $pc.orig
+    cat <<EOF >$pc
+#!/usr/bin/env bash
+unset DYLD_LIBRARY_PATH
+EOF
+    cat $pc.orig >>$pc
+    chmod +x $pc
 else
     export CFLAGS="-std=gnu99 $CFLAGS"
     export RUSTFLAGS="-C link-args=-Wl,-rpath-link,$PREFIX/lib"