tools/pkgconf: Run pkg-config wrapper through shellcheck

Mainly quoting fixes.

Separated parameters by \ for easier readability.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

tools/pkgconf/files/pkg-config

@@ -1,3 +1,6 @@
 #!/bin/sh
 
-pkg-config.real --define-variable=prefix=${STAGING_PREFIX} --define-variable=exec_prefix=${STAGING_PREFIX} --define-variable=bindir=${STAGING_PREFIX}/bin $@
+pkg-config.real \
+--define-variable=prefix="${STAGING_PREFIX}" \
+--define-variable=exec_prefix="${STAGING_PREFIX}" \
+--define-variable=bindir="${STAGING_PREFIX}/bin" "$@"