Update default compiler flags

Enable -fno-semantic-interposition by default
Add off by default define for -fno-common
Reference #164

README.md

@@ -79,16 +79,6 @@ Regardless of which approach you choose, you should ensure that `CXXFLAGS` is se
 and your Portage profile's `LDFLAGS` are respected.  I also enable `-Wl,--hash-style=gnu` as it
 can help catch packages that don't respect `LDFLAGS`, but this is optional.
 
-Additionally, you may want to set environment variables for other languages compiled by GCC as well, for
-cross-language LTO:
-
-~~~
-FCFLAGS="${CFLAGS}"
-FFLAGS="${CFLAGS}"
-OBJCFLAGS="${CFLAGS}"
-OBJCXXFLAGS="${CFLAGS}"
-~~~
-
 It is strongly recommended to use the latest GCC (8.2.0 at the time of writing), latest binutils (2.31.1 currently), and latest glibc (2.28 currently).
 
 When you find a problem, whether it's a package not playing nice with -O3, Graphite, or LTO, consider opening an issue here or sending a pull request with the overrides needed to get the package working.  Over time, we should be able to achieve full coverage of `/usr/portage` this way and provide a one size fits all solution, and not to mention help improve some open source software through the bug reports that will no doubt be generated! 

sys-config/ltoize/files/make.conf.lto

@@ -23,16 +23,6 @@
 
 #CXXFLAGS="${CFLAGS}"
 
-#In addition, you may want to modify the environment variables for other languages compiled with GCC as well:
-
-#FCFLAGS="${CFLAGS}"
-#FFLAGS="${CFLAGS}"
-#OBJCFLAGS="${CFLAGS}"
-#OBJCXXFLAGS="${CFLAGS}"
-
-#This list is pulled from the autotools documentation:
-#https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Environment-Variable-Index.html
-
 #Your LDFLAGS should contain *ALL* of your CFLAGS for LTO to work.  It must receieve all optimization options, march, etc.
 #package.cflags takes care of this for you--no need to manually add your {C,CXX}FLAGS here.
 #It's usually a good idea to enable -Wl,--hash-style=gnu as well to help find packages which don't respect LDFLAGS
@@ -81,7 +71,7 @@ source make.conf.lto.defines
 
 #Thanks to issue #49, no action necessary for preventing stripping of static libraries
 
-CFLAGS="-O3 ${GRAPHITE} ${IPA} ${FLTO} -fuse-linker-plugin"
+CFLAGS="-O3 ${GRAPHITE} ${IPA} ${SEMINTERPOS} ${FLTO} -fuse-linker-plugin"
 
 #Your CXXFLAGS should be a superset of your CFLAGS.  Most people will never need to add anything extra to their CXXFLAGS.
 #CXXFLAGS="${CFLAGS}"

sys-config/ltoize/files/make.conf.lto.defines

@@ -33,3 +33,12 @@ IPA="-fipa-pta"
 #IPA contains -fipa* opts that are disabled by default in GCC.  These are interprocedural optimizations.  For now this is only -fipa-pta.
 #This option increases compile times, but can potentially produce better binaries, especially with LTO.
 #Essentially, it allows the compiler to look into called function bodies when performing alias analysis
+
+SEMINTERPOS="-fno-semantic-interposition"
+
+# With -fno-semantic-interposition the compiler assumes that if interposition happens for functions the overwriting function will have precisely the same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak.
+
+NOCOMMON="-fno-common"
+
+# This option only affects C code.  Only non-conformant C code needs -fcommon, which is enabled by default.  Clear Linux leaves this flag off by default.
+# We may enable this at some point.  For now, there's a lot of breakages to work through.