use %bcond_with to disable brainpool curves

The `%bcond_with` macro allows others to rebuild the package with the
brainpool curves enabled by passing `--with brainpool` to `rpmbuild`.

libgcrypt.spec

@@ -13,6 +13,8 @@ sha256sum:close()
 print(string.sub(hash, 0, 16))
 }
 
+# disable brainpool curves by default
+%bcond_with brainpool
 
 Name: libgcrypt
 Version: 1.10.1
@@ -83,7 +85,7 @@ autoreconf -f
 %endif
      --enable-noexecstack \
      --enable-hmac-binary-check=%{hmackey} \
-     --disable-brainpool \
+     %{!?with_brainpool:--disable-brainpool} \
      --enable-digests="$DIGESTS" \
      --enable-ciphers="$CIPHERS" \
      --with-fips-module-version="$FIPS_MODULE_NAME %{version}-%{srpmhash}"
@@ -178,6 +180,7 @@ mkdir -p -m 755 $RPM_BUILD_ROOT/etc/gcrypt
 %changelog
 * Sun May 29 2022 Todd Zullinger <tmz@pobox.com> - 1.10.1-3
 - improve --disable-brainpool configure output
+- use %%bcond_with to disable brainpool curves
 
 * Fri Apr 08 2022 Jakub Jelen <jjelen@redhat.com> - 1.10.1-2
 - Adjust integrity check creation to match upstream (#2073018)