[PATCH 0/4] Fix library testsuite compilation for build sysroot

["Maciej W. Rozycki" <macro@wdc.com>]

Hi,

 This patch series addresses a problem with the testsuite compiler being 
set up across libatomic, libffi, libgo, libgomp with no correlation 
whatsoever to the target compiler being used in GCC compilation.  
Consequently there in no arrangement made to set up the compilation 
sysroot according to the build sysroot specified for GCC compilation, 
causing a catastrophic failure across the testsuites affected from the 
inability to link executables.

 The fix is based on a similar arrangement already made for passing 
autoconf output variables in libgomp, and uses the GCC_UNDER_TEST (or 
GOC_UNDER_TEST, as applicable) TCL variable already used across several 
GCC library testsuites.

 Verified with a cross-compiler configured for the `riscv-linux-gnu' 
target and the `x86_64-linux-gnu' host and using RISC-V/Linux QEMU in the 
user emulation mode as the target board.  Also no change in results with 
`x86_64-linux-gnu' native regression testing.

 See individual change descriptions for details.

 OK to apply to the GCC repo (for libraries maintained externally I'll be 
happy to assist with any merging required, although given that these 
changes are confined to autoconf/automake scriptery they should be 
straightforward to apply, barring any conflicts in generated files)?

  Maciej