add --without doc option

because EL8 does not have necessary build dependencies yet,
sphinx3-breathe and nodejs-less, for instance. so add
"--without doc" option to disable the doc build.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>

fmt.spec

@@ -1,3 +1,4 @@
+%bcond_without doc
 Name:           fmt
 Version:        6.2.0
 Release:        2%{?dist}
@@ -23,7 +24,7 @@ BuildRequires:  cmake3
 %else
 BuildRequires:  cmake
 %endif
-# For building documentation
+%if %{with doc}
 BuildRequires:  doxygen
 BuildRequires:  nodejs-less
 %if 0%{?rhel} && 0%{?rhel} <= 7
@@ -33,6 +34,7 @@ BuildRequires:  python%{python3_version_nodots}-breathe
 BuildRequires:  python3-sphinx
 BuildRequires:  python3-breathe
 %endif
+%endif
 
 # This package replaces the old name of cppformat
 Provides:       cppformat = %{version}-%{release}
@@ -53,6 +55,7 @@ Obsoletes:      cppformat-devel < %{version}-%{release}
 %description    devel
 This package contains the header file for using %{name}.
 
+%if %{with doc}
 %package        doc
 Summary:        Documentation files for %{name}
 License:        Python
@@ -64,6 +67,7 @@ Obsoletes:      cppformat-doc < %{version}-%{release}
 
 %description    doc
 This package contains documentation for developer documentation for %{name}.
+%endif
 
 %prep
 %autosetup -p1
@@ -81,11 +85,13 @@ pushd build
     -DFMT_CMAKE_DIR=%{_datadir}/cmake/%{name} \
     -DFMT_LIB_DIR=%{_libdir}
 
+%if %{with doc}
 # Remove --clean-css since that plugin isn't available
 sed -i "s/'--clean-css',//" ../doc/build.py
 %make_build all doc
 # Remove temporary build products
 rm -rf ../build/doc/html/{.buildinfo,.doctrees,objects.inv}
+%endif
 
 %install
 %make_install -C build
@@ -106,9 +112,11 @@ popd
 %{_datadir}/cmake/%{name}
 %{_libdir}/pkgconfig/%{name}.pc
 
+%if %{with doc}
 %files doc
 %doc %{_datadir}/doc/%{name}
 %license doc/python-license.txt
+%endif
 
 %changelog
 * Thu Apr 30 2020 Kefu Chai <tchaikov@gmail.com> - 6.2.0-2