https://sourceforge.net/p/xmlrpc-c/code/3152
https://bugs.gentoo.org/870253
--- a/configure
+++ b/configure
@@ -5974,11 +5974,11 @@
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for OpenSSL library" >&5
 $as_echo_n "checking for OpenSSL library... " >&6; }

-if pkg-config openssl; then
-  HAVE_OPENSSL=yes
-  OPENSSL_LDADD=$(pkg-config openssl --libs)
-
-  OPENSSL_CFLAGS=$(pkg-config openssl --cflags)
+if ${PKG_CONFIG} openssl; then
+  HAVE_OPENSSL=yes
+  OPENSSL_LDADD=$(${PKG_CONFIG} openssl --libs)
+ 
+  OPENSSL_CFLAGS=$(${PKG_CONFIG} 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