CMake: use -O1 instead of -O2 for building generated .c code

Idea here is that this is a sweet spot of not wasting time waiting for
optimizations but also getting decent runime performance.

Author: andrewrk

CMakeLists.txt

@@ -713,8 +713,8 @@ if(MSVC)
   set(ZIG2_COMPILE_FLAGS "/std:c99")
   set(ZIG2_LINK_FLAGS "/STACK:16777216")
 else()
-  set(ZIG1_COMPILE_FLAGS "-std=c99 -O2 -march=native")
-  set(ZIG2_COMPILE_FLAGS "-std=c99 -O2 -march=native")
+  set(ZIG1_COMPILE_FLAGS "-std=c99 -O1 -march=native")
+  set(ZIG2_COMPILE_FLAGS "-std=c99 -O1 -march=native")
   set(ZIG2_LINK_FLAGS "-Wl,-z,stack-size=0x10000000")
 endif()