[PATCH] Make pkg-config files cross-compile friendly

Currently the pc files use hard coded paths for "includedir" and
"libdir."

Example:

Cflags: -I/usr/include
Libs: -L/usr/lib -lpq

This is not very fortunate when cross compiling inside a buildroot,
where the includes and libs are inside a staging directory, because this
introduces host paths into the build:

checking for pkg-config... /builder/shared-workdir/build/sdk/staging_dir/host/bin/pkg-config
checking for PostgreSQL libraries via pkg_config... -L/usr/lib <----

This commit addresses this by doing the following two things:

1. Instead of hard coding the paths in "Cflags" and "Libs"
"${includedir}" and "${libdir}" are used. Note: these variables can
be overriden on the pkg-config command line
("--define-variable=libdir=/some/path").

2. Add the variables "prefix" and "exec_prefix". If "includedir"
and/or "libdir" are using these then construct them accordingly.
This is done because buildroots (for instance OpenWrt) tend to
rename the real pkg-config and call it indirectly from a script
that sets "prefix", "exec_prefix" and "bindir", like so:

pkg-config.real --define-variable=prefix=${STAGING_PREFIX} \
--define-variable=exec_prefix=${STAGING_PREFIX} \
--define-variable=bindir=${STAGING_PREFIX}/bin $@

Example #1: user calls ./configure with "--libdir=/some/lib" and
"--includedir=/some/include":

prefix=/usr/local/pgsql
exec_prefix=/usr/local/pgsql
includedir=/some/include
libdir=/some/lib

Name: libpq
Description: PostgreSQL libpq library
Url: http://www.postgresql.org/
Version: 12.1
Requires:
Requires.private:
Cflags: -I${includedir}
Libs: -L${libdir} -lpq
Libs.private: -lcrypt -lm

Example #2: user calls ./configure with no arguments:

prefix=/usr/local/pgsql
exec_prefix=/usr/local/pgsql
includedir=${prefix}/include
libdir=${exec_prefix}/lib

Name: libpq
Description: PostgreSQL libpq library
Url: http://www.postgresql.org/
Version: 12.1
Requires:
Requires.private:
Cflags: -I${includedir}
Libs: -L${libdir} -lpq
Libs.private: -lcrypt -lm

Like this the paths can be forced into the staging directory when using
a buildroot setup:

checking for pkg-config... /home/sk/tmp/openwrt/staging_dir/host/bin/pkg-config
checking for PostgreSQL libraries via pkg_config... -L/home/sk/tmp/openwrt/staging_dir/target-mips_24kc_musl/usr/lib

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>
---
src/Makefile.shlib | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/Makefile.shlib b/src/Makefile.shlib
index 29a7f6d38c..33c23dabdd 100644
--- a/src/Makefile.shlib
+++ b/src/Makefile.shlib
@@ -387,14 +387,27 @@ endif # PORTNAME == cygwin || PORTNAME == win32

 %.pc: $(MAKEFILE_LIST)
-	echo 'Name: lib$(NAME)' >$@
+	echo 'prefix=$(prefix)' >$@
+	echo 'exec_prefix=$(exec_prefix)' >>$@
+ifeq ($(patsubst $(prefix)/%,,$(includedir)),)
+	echo 'includedir=$${prefix}/$(patsubst $(prefix)/%,%,$(includedir))' >>$@
+else
+	echo 'includedir=$(includedir)' >>$@
+endif
+ifeq ($(patsubst $(exec_prefix)/%,,$(libdir)),)
+	echo 'libdir=$${exec_prefix}/$(patsubst $(exec_prefix)/%,%,$(libdir))' >>$@
+else
+	echo 'libdir=$(libdir)' >>$@
+endif
+	echo >>$@
+	echo 'Name: lib$(NAME)' >>$@
 	echo 'Description: PostgreSQL lib$(NAME) library' >>$@
 	echo 'Url: $(PACKAGE_URL)' >>$@
 	echo 'Version: $(VERSION)' >>$@
 	echo 'Requires: ' >>$@
 	echo 'Requires.private: $(PKG_CONFIG_REQUIRES_PRIVATE)' >>$@
-	echo 'Cflags: -I$(includedir)' >>$@
-	echo 'Libs: -L$(libdir) -l$(NAME)' >>$@
+	echo 'Cflags: -I$${includedir}' >>$@
+	echo 'Libs: -L$${libdir} -l$(NAME)' >>$@
 # Record -L flags that the user might have passed in to the PostgreSQL
 # build to locate third-party libraries (e.g., ldap, ssl).  Filter out
 # those that point inside the build or source tree.  Use sort to
--
2.24.1