PR85678: Change default to -fno-common

PR85678: Change default to -fno-common

GCC currently defaults to -fcommon.  As discussed in the PR, this is an ancient
C feature which is not conforming with the latest C standards.  On many targets
this means global variable accesses have a codesize and performance penalty.
This applies to C code only, C++ code is not affected by -fcommon.  It is about
time to change the default.

    gcc/
	PR85678
	* common.opt (fcommon): Change init to 1.
	* invoke.texi (-fcommon): Update documentation.

    testsuite/
	* g++.dg/lto/odr-6_1.c: Add -fcommon.
	* gcc.dg/alias-15.c: Likewise.
	* gcc.dg/fdata-sections-1.c: Likewise.
	* gcc.dg/ipa/pr77653.c: Likewise.
	* gcc.dg/lto/20090729_0.c: Likewise.
	* gcc.dg/lto/20111207-1_0.c: Likewise.
	* gcc.dg/lto/c-compatible-types-1_0.c: Likewise.
	* gcc.dg/lto/pr55525_0.c: Likewise.
	* gcc.dg/lto/pr88077_0.c: Use long to avoid alignment warning.
	* gcc.dg/lto/pr88077_1.c: Add -fcommon.
	* gcc.target/aarch64/sve/peel_ind_1.c: Allow ANCHOR0.
	* gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
	* gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
	* gcc.target/i386/volatile-bitfields-2.c: Allow movl or movq.

From-SVN: r278509