Initialize contents of dolfin.pc correctly

(rhbz#2118536)

dolfin.spec

@@ -29,6 +29,7 @@ ExcludeArch:    %{ix86}
 BuildRequires:  gcc-c++
 BuildRequires:  gnupg2
 BuildRequires:  cmake
+BuildRequires:  pkgconf
 BuildRequires:  boost-devel
 BuildRequires:  eigen3-devel
 BuildRequires:  petsc-devel
@@ -66,6 +67,9 @@ FEniCS Problem Solving Environment.}
 %package devel
 Summary:        Development files for %{name}
 Requires:       %{name} = %{version}-%{release}%{?isa}
+# dolfin headers include headers from other projects
+Requires:       boost-devel
+Requires:       eigen3-devel
 
 %description devel
 %{summary}.
@@ -115,6 +119,15 @@ CFLAGS="%{optflags} -Wno-unused-variable -DH5_USE_110_API" CXXFLAGS="%{optflags}
   -Wno-dev
 %make_build
 
+# The flags defined in the pkg-config file are used at runtime.
+# For some reason, the contents are not injected properly.
+# https://fenicsproject.discourse.group/t/cant-define-expression-through-c-returns-fatal-error-ufc-h-no-such-file-or-directory/5472/19
+# https://bugzilla.redhat.com/show_bug.cgi?id=2118536
+ffc_path="$(python3 -c 'import ffc; print(ffc.get_include_path())')"
+eigen_options="$(pkgconf --cflags eigen3)"
+sed -r -i "s|Cflags:.*|\\0 -I${ffc_path} ${eigen_options}|" \
+    dolfin.pc
+
 # "temporary install" so the python build can find the stuff it needs
 %make_install