ci: switch to pkgconf on Linux too

Change-Id: I056f85a1bf2fdc6167c7c2d39c664b5c32c20b98
diff --git a/.jenkins.d/40-headers-check.sh b/.jenkins.d/40-headers-check.sh
index 958559e..1ef8cb9 100755
--- a/.jenkins.d/40-headers-check.sh
+++ b/.jenkins.d/40-headers-check.sh
@@ -17,8 +17,8 @@
 
 CXX=${CXX:-g++}
 STD=-std=c++17
-CXXFLAGS="-O2 -Wall -Wno-unknown-warning-option -Wno-enum-constexpr-conversion -Wno-unused-const-variable $(pkg-config --cflags libndn-cxx $PCFILE)"
-INCLUDEDIR="$(pkg-config --variable=includedir $PCFILE)"/$PROJ
+CXXFLAGS="-O2 -Wall -Wno-unknown-warning-option -Wno-enum-constexpr-conversion -Wno-unused-const-variable $(pkgconf --cflags libndn-cxx $PCFILE)"
+INCLUDEDIR="$(pkgconf --variable=includedir $PCFILE)"/$PROJ
 
 echo "Using: $CXX $STD $CXXFLAGS"