https://sourceforge.net/p/xmlrpc-c/code/3152
https://bugs.gentoo.org/870253
--- a/configure.in
+++ b/configure.in
@@ -696,11 +696,11 @@ dnl =======================================================================
 
 AC_MSG_CHECKING(for OpenSSL library)
 
-if pkg-config openssl; then
+if ${PKG_CONFIG} openssl; then
   HAVE_OPENSSL=yes
-  OPENSSL_LDADD=$(pkg-config openssl --libs)
+  OPENSSL_LDADD=$(${PKG_CONFIG} openssl --libs)
   AC_SUBST(OPENSSL_LDADD)
-  OPENSSL_CFLAGS=$(pkg-config openssl --cflags)
+  OPENSSL_CFLAGS=$(${PKG_CONFIG} openssl --cflags)
   AC_SUBST(OPENSSL_CFLAGS)
 else
   HAVE_OPENSSL=no

--- a/config.mk.in
+++ b/config.mk.in
@@ -59,6 +59,8 @@
 C_COMPILER_GNU = @C_COMPILER_GNU@
 CXX_COMPILER_GNU = @CXX_COMPILER_GNU@
 
+PKG_CONFIG ?= pkg-config
+
 # Stuff 'configure' figured out via AC_CANONICAL_HOST macro in configure.in
 # and config.guess program and 'configure' command options:

--- a/lib/openssl/Makefile
+++ b/lib/openssl/Makefile
@@ -25,8 +25,8 @@
 
 MAJ := 1
 
-OPENSSL_INCLUDES := $(shell pkg-config openssl --cflags)
-OPENSSL_LIBS     := $(shell pkg-config openssl --libs)
+OPENSSL_INCLUDES := $(shell $(PKG_CONFIG) openssl --cflags)
+OPENSSL_LIBS     := $(shell $(PKG_CONFIG) openssl --libs)
 
 include $(SRCDIR)/common.mk