BUILD: makefile: remove -fomit-frame-pointer optimisation (solaris)

-fomit-frame-pointer is commonly avoided because tools like dtrace
needs frame-pointer. Remove it from Makefile and let builder's env
do the job.

This patch could be backported to 1.9.
diff --git a/Makefile b/Makefile
index 04451cd..fcd1581 100644
--- a/Makefile
+++ b/Makefile
@@ -353,7 +353,7 @@
   set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_CRYPT_H USE_GETADDRINFO USE_THREAD \
     USE_OBSOLETE_LINKER)
-  TARGET_CFLAGS  = -fomit-frame-pointer -DFD_SETSIZE=65536 -D_REENTRANT -D_XOPEN_SOURCE=500 -D__EXTENSIONS__
+  TARGET_CFLAGS  = -DFD_SETSIZE=65536 -D_REENTRANT -D_XOPEN_SOURCE=500 -D__EXTENSIONS__
   TARGET_LDFLAGS = -lnsl -lsocket
 endif