Changes to the /usr/lib/64/R/etc/Makeconf file to use the
GNU C, C++ and Fortran compilers. These are applied to the
Makeconf file in the prototype build area as a post install
action in the Makefile.

--- Makeconf.GNU.orig	2016-03-30 18:48:11.403166611 -0700
+++ Makeconf.GNU	2016-03-30 18:53:12.985544279 -0700
@@ -13,38 +13,38 @@
 ## Used by packages 'maps' and 'mapdata'
 AWK = gawk
 BLAS_LIBS = -lsunperf
-C_VISIBILITY = 
-CC = cc
-CFLAGS = -m64 -xO3 -xc99=all -xlibmieee $(LTO)
-CPICFLAGS = -KPIC -DPIC
+C_VISIBILITY = -fvisibility=hidden
+CC = gcc -std=gnu99
+CFLAGS = -g -O2 -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2 $(LTO)
+CPICFLAGS = -fpic
 CPPFLAGS = -m64
-CXX = CC
+CXX = g++
 CXXCPP = $(CXX) -E
-CXXFLAGS = -norunpath -m64 -xO3 -std=c++11 -D__MATHERR_RENAME_EXCEPTION $(LTO)
-CXXPICFLAGS = -KPIC
-CXX1X = CC
-CXX1XFLAGS = -norunpath -m64 -xO3 -std=c++11 -D__MATHERR_RENAME_EXCEPTION
-CXX1XPICFLAGS = -KPIC
-CXX1XSTD =  
+CXXFLAGS = -m64 -g -O2 -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2 $(LTO)
+CXXPICFLAGS = -fpic
+CXX1X = g++
+CXX1XFLAGS = -m64 -g -O2 -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2
+CXX1XPICFLAGS = -fpic
+CXX1XSTD = -std=c++11
 DYLIB_EXT = .so
 DYLIB_LD = $(CC)
-DYLIB_LDFLAGS = -G -fopenmp# $(CFLAGS) $(CPICFLAGS)
+DYLIB_LDFLAGS = -shared -fopenmp# $(CFLAGS) $(CPICFLAGS)
 DYLIB_LINK = $(DYLIB_LD) $(DYLIB_LDFLAGS) $(LDFLAGS)
 ECHO = echo
 ECHO_C = \c
 ECHO_N = 
 ECHO_T = 
 ## NB, set FC before F77 as on Solaris make, setting FC sets F77
-FC = f95 -m64
-FCFLAGS = -xO3 -m64 $(LTO)
+FC = gfortran -m64
+FCFLAGS = -g -O2 -m64 $(LTO)
 ## additional libs needed when linking with $(FC), e.g. on Solaris
 FCLIBS = -lsunperf -lfsu -lsunmath
-F77 = f95 -m64
-F77_VISIBILITY = 
-FFLAGS = -xO3 -m64 $(LTO)
-FLIBS = -lsunperf -lfsu -lsunmath
-FCPICFLAGS = -PIC
-FPICFLAGS = -KPIC -DPIC
+F77 = gfortran -m64
+F77_VISIBILITY = -fvisibility=hidden
+FFLAGS = -g -O2 -m64 $(LTO)
+FLIBS = -lsunperf -lfsu -lsunmath -lgfortran -lm -lquadmath
+FCPICFLAGS = -fpic
+FPICFLAGS = -fpic
 FOUNDATION_CPPFLAGS = 
 FOUNDATION_LIBS = 
 JAR = /usr/bin/jar
@@ -68,11 +68,11 @@
 ## needed by R CMD config
 LIBnn = lib
 LIBTOOL = $(SHELL) "$(R_HOME)/bin/libtool"
-LDFLAGS = -norunpath -m64 -KPIC -DPIC -lc -L/usr/lib/studio/64 -R/usr/lib/studio/64 -lsunperf -lfsu -lmtsk -lpicl -lkstat -L/usr/lib/64/R/lib -R/usr/lib/64/R/lib
+LDFLAGS = -m64 -fpic -lc -L/usr/lib/studio/64 -R/usr/lib/studio/64 -lsunperf -lfsu -lmtsk -lpicl -lkstat -L/usr/lib/64/R/lib -R/usr/lib/64/R/lib
 LTO = 
 ## needed to build applications linking to static libR
 MAIN_LD = $(CC)
-MAIN_LDFLAGS = -fopenmp
+MAIN_LDFLAGS = -Wl,--export-dynamic -fopenmp
 MAIN_LINK = $(MAIN_LD) $(MAIN_LDFLAGS) $(LDFLAGS)
 MKINSTALLDIRS = $(R_HOME)/bin/mkinstalldirs
 OBJC = gcc
@@ -81,21 +81,21 @@
 OBJCXX = 
 R_ARCH = 
 RANLIB = ranlib
-SAFE_FFLAGS = -xO3 -m64
+SAFE_FFLAGS = -g -O2 -m64 -ffloat-store
 SED = /usr/xpg4/bin/sed
 SHELL = /bin/bash
 SHLIB_CFLAGS = 
 SHLIB_CXXFLAGS = 
 SHLIB_CXXLD = $(CXX)
-SHLIB_CXXLDFLAGS = -lCrunG3 -G
+SHLIB_CXXLDFLAGS = -shared
 SHLIB_CXX1XLD = $(CXX1X) $(CXX1XSTD)
-SHLIB_CXX1XLDFLAGS = -lCrunG3 -G
+SHLIB_CXX1XLDFLAGS = -shared
 SHLIB_EXT = .so
 SHLIB_FCLD = $(FC)
-SHLIB_FCLDFLAGS = -G
+SHLIB_FCLDFLAGS = -shared
 SHLIB_FFLAGS = 
 SHLIB_LD = $(CC)
-SHLIB_LDFLAGS = -G# $(CFLAGS) $(CPICFLAGS)
+SHLIB_LDFLAGS = -shared# $(CFLAGS) $(CPICFLAGS)
 SHLIB_LIBADD = 
 ## We want to ensure libR is picked up from $(R_HOME)/lib
 ## before e.g. /usr/local/lib if a version is already installed.