[Bug bootstrap/54419] [4.8 Regression] Compiling libstdc++-v3/src/c++11/random.cc fails on platforms not knowing rdrand

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54419

--- Comment #34 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-09-05 12:40:49 UTC ---
No, the #c24 and #c25 comments make no sense at all.
In void f(void) { asm ("rdrand %eax"); } rdrand shouldn't be optimized out, at
least not by gcc, asm in this case is implicitly volatile.  AC_TRY_RUN is not
desirable for many reasons, as has been said and you can read in the code, the
runtime detection is done in libstdc++ code (ctor which uses cpuid), all
configury should test is whether assembler is able to assemble rdrand.
Furthermore, never patch configure, you need to patch configure.ac resp.
configure.in instead.