Use make_build macro and remove hard-coded gcc

https://docs.fedoraproject.org/en-US/packaging-guidelines/#_parallel_make

ftp.spec

@@ -1,7 +1,7 @@
 Summary: The standard UNIX FTP (File Transfer Protocol) client
 Name: ftp
 Version: 0.17
-Release: 84%{?dist}
+Release: 85%{?dist}
 License: BSD with advertising
 Source0: ftp://ftp.linux.org.uk/pub/linux/Networking/netkit/netkit-ftp-%{version}.tar.gz
 URL: ftp://ftp.linux.org.uk/pub/linux/Networking/netkit
@@ -91,7 +91,7 @@ file transfers.
 %patch35 -p1 -b .linelen-segfault
 
 %build
-sh configure --with-c-compiler=gcc --enable-ipv6
+sh configure --with-c-compiler=%{__cc} --enable-ipv6
 perl -pi -e '
     s,^CC=.*$,CC=cc,;
     s,-O2,\$(RPM_OPT_FLAGS) -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64,;
@@ -101,7 +101,7 @@ perl -pi -e '
     s,^SBINDIR=.*$,SBINDIR=%{_sbindir},;
     ' MCONFIG
 
-make %{?_smp_mflags}
+%{make_build}
 
 %install
 mkdir -p ${RPM_BUILD_ROOT}%{_bindir}
@@ -118,6 +118,10 @@ make INSTALLROOT=${RPM_BUILD_ROOT} install
 %{_mandir}/man5/netrc.*
 
 %changelog
+* Thu Nov 19 2020 Michal Ruprich <mruprich@redhat.com> - 0.17-85
+- Use make_build macro and remove hard-coded gcc
+- https://docs.fedoraproject.org/en-US/packaging-guidelines/#_parallel_make
+
 * Mon Jul 27 2020 Fedora Release Engineering <releng@fedoraproject.org> - 0.17-84
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_33_Mass_Rebuild