Add builder for whereami (#9473)

* Add builder for whereami

Cross-platform library for identifying where on the filesystem the
current executable lives.

* mkdir -p

* [whereami] Windows doesn't like -ldl

* [whereami] Only -ldl with glibc, + how did I forget the input to cc

* Update W/WhereAmI/build_tarballs.jl

W/WhereAmI/build_tarballs.jl

@@ -0,0 +1,32 @@
+using BinaryBuilder
+
+name = "WhereAmI"
+version = v"1.0.0"  # no proper versions/releases, this is made up
+
+sources = [
+    GitSource("https://github.com/gpakosz/whereami",
+              "dcb52a058dc14530ba9ae05e4339bd3ddfae0e0e"),
+]
+
+script = raw"""
+cd ${WORKSPACE}/srcdir/whereami/
+mkdir -p "${libdir}"
+FLAGS=(-Isrc -O2 -std=c99 -fPIC)
+if [[ "${target}" == *-gnu* ]]; then
+    FLAGS+=(-ldl)
+fi
+cc src/whereami.c ${FLAGS[@]} -shared -o "${libdir}/libwai.${dlext}"
+install -Dvm 644 src/whereami.h "${includedir}/whereami.h"
+install_license LICENSE.MIT
+"""
+
+platforms = supported_platforms()
+
+products = [
+    LibraryProduct("libwai", :libwai),
+]
+
+dependencies = Dependency[]
+
+build_tarballs(ARGS, name, version, sources, script, platforms, products, dependencies;
+               julia_compat="1.6")