Disable strict aliasing on clang (nim-lang#25067)

Workaround for nim-lang#24596.

I also took the liberty to disable it on all targets with GCC, since
their documentation claims that it is also enabled on -Os.

---------

Co-authored-by: ringabout <[email protected]>

Author: bptato

config/nim.cfg

@@ -257,10 +257,12 @@ clang.objc.options.linker = "-lobjc -lgnustep-base"
   gcc.options.linker %= "-L $WIND_BASE/target/lib/usr/lib/ppc/PPC32/common -mrtp -fno-strict-aliasing -D_C99 -D_HAS_C9X -std=c99 -fasm -Wall -Wno-write-strings"
 @end
 
+# seqs_v2 violates strict aliasing.
+gcc.options.always %= "${gcc.options.always} -fno-strict-aliasing"
 # -fno-math-errno is default in OSX, iOS, BSD, Musl, Libm, LLVM, Clang, ICC.
 # See https://itnext.io/why-standard-c-math-functions-are-slow-d10d02554e33
 # and https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Optimize-Options.html#Optimize-Options
-gcc.options.speed = "-O3 -fno-strict-aliasing -fno-ident -fno-math-errno"
+gcc.options.speed = "-O3 -fno-ident -fno-math-errno"
 gcc.options.size = "-Os -fno-ident"
 @if windows:
   gcc.options.debug = "-g3 -Og -gdwarf-3"
@@ -281,7 +283,7 @@ llvm_gcc.options.size = "-Os"
 # Configuration for the LLVM CLang compiler:
 clang.options.debug = "-g"
 clang.cpp.options.debug = "-g"
-clang.options.always = "-w -ferror-limit=3"
+clang.options.always = "-w -ferror-limit=3 -fno-strict-aliasing"
 clang.options.speed = "-O3"
 clang.options.size = "-Os"