BUILD: makefile: make all OpenSSL variants use the same settings

It's getting complicated to configure includes and lib dirs for
OpenSSL API variants such as WolfSSL, because some settings are
common and others are specific but carry a prefix that doesn't
match the USE_* rule scheme.

This patch simplifies everything by considering that all SSL libs
will use SSL_INC, SSL_LIB, SSL_CFLAGS and SSL_LDFLAGS. That's much
more convenient. This works thanks to the settings collector which
explicitly checks the SSL_* settings. When USE_OPENSSL_WOLFSSL is
set, then USE_OPENSSL is implied, so that there's no need to
duplicate maintenance effort.
diff --git a/Makefile b/Makefile
index 802263c..a5ddc70 100644
--- a/Makefile
+++ b/Makefile
@@ -108,8 +108,6 @@
 #                                                               pcre2-config)
 #   SSL_LIB        : force the lib path to libssl/libcrypto
 #   SSL_INC        : force the include path to libssl/libcrypto
-#   WOLFSSL_INC    : force the include path to wolfSSL
-#   WOLFSSL_LIB    : force the lib path to wolfSSL
 #   LUA_LIB        : force the lib path to lua
 #   LUA_INC        : force the include path to lua
 #   LUA_LIB_NAME   : force the lib name (or automatically evaluated, by order of
@@ -558,24 +556,29 @@
   OPTIONS_OBJS   += src/cpuset.o
 endif
 
+# OpenSSL is packaged in various forms and with various dependencies.
+# In general -lssl is enough, but on some platforms, -lcrypto may be needed,
+# reason why it's added by default. Some even need -lz, then you'll need to
+# pass it in the "ADDLIB" variable if needed. If your SSL libraries are not
+# in the usual path, use SSL_INC=/path/to/inc and SSL_LIB=/path/to/lib.
+
+# This is for the WolfSSL variant of the OpenSSL API. Setting it implies
+# OPENSSL so it's not necessary to set the latter.
+ifneq ($(USE_OPENSSL_WOLFSSL),)
+  SSL_CFLAGS      := $(if $(SSL_INC),-I$(SSL_INC) -I$(SSL_INC)/wolfssl)
+  SSL_LDFLAGS     := $(if $(SSL_LIB),-L$(SSL_LIB)) -lwolfssl
+  # always automatically set USE_OPENSSL
+  USE_OPENSSL     := $(if $(USE_OPENSSL),$(USE_OPENSSL),implicit)
+endif
+
+# This is for any variant of the OpenSSL API. By default it uses OpenSSL.
 ifneq ($(USE_OPENSSL),)
-  # OpenSSL is packaged in various forms and with various dependencies.
-  # In general -lssl is enough, but on some platforms, -lcrypto may be needed,
-  # reason why it's added by default. Some even need -lz, then you'll need to
-  # pass it in the "ADDLIB" variable if needed. If your SSL libraries are not
-  # in the usual path, use SSL_INC=/path/to/inc and SSL_LIB=/path/to/lib.
+  # only preset these for the regular openssl
   ifeq ($(USE_OPENSSL_WOLFSSL),)
-    OPENSSL_CFLAGS   = $(if $(SSL_INC),-I$(SSL_INC))
-    OPENSSL_LDFLAGS  = $(if $(SSL_LIB),-L$(SSL_LIB)) -lssl -lcrypto
+    SSL_CFLAGS    := $(if $(SSL_INC),-I$(SSL_INC))
+    SSL_LDFLAGS   := $(if $(SSL_LIB),-L$(SSL_LIB)) -lssl -lcrypto
   endif
-  OPTIONS_OBJS  += src/ssl_sock.o src/ssl_ckch.o src/ssl_sample.o src/ssl_crtlist.o src/cfgparse-ssl.o src/ssl_utils.o src/jwt.o src/ssl_ocsp.o
-endif
-
-ifneq ($(USE_OPENSSL_WOLFSSL),)
-  WOLFSSL_CFLAGS    = $(if $(WOLFSSL_INC),-I$(WOLFSSL_INC) -I$(WOLFSSL_INC)/wolfssl)
-  WOLFSSL_LDFLAGS   = $(if $(WOLFSSL_LIB),-L$(WOLFSSL_LIB)) -lwolfssl
-  OPTIONS_CFLAGS   += $(WOLFSSL_CFLAGS)
-  OPTIONS_LDFLAGS  += $(WOLFSSL_LDFLAGS)
+  OPTIONS_OBJS += src/ssl_sock.o src/ssl_ckch.o src/ssl_sample.o src/ssl_crtlist.o src/cfgparse-ssl.o src/ssl_utils.o src/jwt.o src/ssl_ocsp.o
 endif
 
 ifneq ($(USE_ENGINE),)