Implemented out of source build.

fmt.spec

@@ -1,3 +1,5 @@
+%undefine __cmake_in_source_build
+
 %bcond_without doc
 Name:           fmt
 Version:        7.0.1
@@ -18,6 +20,7 @@ Patch8:         doc-build-use-python3.patch
 
 BuildRequires:  gcc
 BuildRequires:  gcc-c++
+BuildRequires:  ninja-build
 %if 0%{?rhel} && 0%{?rhel} <= 7
 BuildRequires:  cmake3
 %else
@@ -70,15 +73,14 @@ This package contains documentation for developer documentation for %{name}.
 
 %prep
 %autosetup -p1
-mkdir build
 
 %build
-pushd build
 %if 0%{?rhel} && 0%{?rhel} <= 7
-%cmake3 ..                                    \
+%cmake3                                       \
 %else
-%cmake ..                                     \
+%cmake                                        \
 %endif
+    -G Ninja                                  \
     -DCMAKE_BUILD_TYPE=RelWithDebInfo         \
     -DCMAKE_POSITION_INDEPENDENT_CODE=ON      \
     -DFMT_CMAKE_DIR=%{_datadir}/cmake/%{name} \
@@ -86,19 +88,17 @@ pushd build
 
 %if %{with doc}
 # Remove --clean-css since that plugin isn't available
-sed -i "s/'--clean-css',//" ../doc/build.py
-%make_build all doc
+sed -i "s/'--clean-css',//" doc/build.py
+%cmake_build --target all --target doc
 # Remove temporary build products
-rm -rf ../build/doc/html/{.buildinfo,.doctrees,objects.inv}
+rm -rf %{_vpath_builddir}/doc/html/{.buildinfo,.doctrees,objects.inv}
 %endif
 
 %install
-%make_install -C build
+%cmake_install
 
 %check
-pushd build
-ctest -VV %{?_smp_mflags}
-popd
+%ctest
 
 %files
 %license LICENSE.rst