When cross-compiling a package using gnu-build-system,
%build-inputs does not exist. But libgcrypt uses %build-inputs
anyway. Fix it.

* gnu/packages/gnupg.scm
  (libgcrypt)[arguments]<#:configure-flags>: Make this a G-exp
  instead of a raw S-exp. Eliminate %build-inputs and use
  this-package-input instead.
---
 gnu/packages/gnupg.scm | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)