[SymForce] build symforce_gen with -ffast-math

This 1) should be safe and 2) should speed things up, e.g. for things
that rely on Horner's method.  Included an option to turn this off,
although I have it on by default, which I think is a good idea.

Relying on existing tests?  Not sure how confident we are flipping this.
Mostly uploading to run tests for now.

One thing is that this requires we're more careful about repeatedly
normalizing Rot3's, since it seems like that's no longer necessarily
idempotent (and I guess it was before).  That's a performance win anyway
though.

Topic: sym-fast-math
GitOrigin-RevId: 13bcdea25f335d0a6c5527b8b86f61181e4a367d

CMakeLists.txt

@@ -70,14 +70,23 @@ option(SYMFORCE_SKYMARSHAL_PRINTING
 )
 
 # ------------------------------------------------------------------------------
-# Misc
+# Build Customization
 
 option(SYMFORCE_BUILD_STATIC_LIBRARIES "Build libraries as static" OFF)
 
 set(SYMFORCE_COMPILE_OPTIONS -Wall;-Wextra CACHE STRING
   "Extra flags to pass to the compiler; defaults to enabling warnings"
 )
 
+option(SYMFORCE_NO_FAST_MATH "Don't automatically add -ffast-math to some targets" OFF)
+
+set(SYMFORCE_EIGEN_TARGET "Eigen3::Eigen" CACHE STRING
+  "Target to depend on for Eigen. Default is to find Eigen with find_package."
+)
+
+# ------------------------------------------------------------------------------
+# Misc
+
 set(SYMFORCE_PYTHON_OVERRIDE "" CACHE STRING
   "Python executable to use - if empty (the default), find python in the environment"
 )
@@ -98,10 +107,6 @@ set(SYMFORCE_PY_EXTENSION_MODULE_OUTPUT_PATH ${CMAKE_CURRENT_BINARY_DIR}/pybind
   "Location to place generated python extension modules"
 )
 
-set(SYMFORCE_EIGEN_TARGET "Eigen3::Eigen" CACHE STRING
-  "Target to depend on for Eigen. Default is to find Eigen with find_package."
-)
-
 # ==============================================================================
 # Setup
 # ==============================================================================
@@ -281,6 +286,9 @@ add_library(
   ${SYMFORCE_GEN_HEADERS}
 )
 target_compile_options(symforce_gen PRIVATE ${SYMFORCE_COMPILE_OPTIONS})
+if(NOT SYMFORCE_NO_FAST_MATH)
+  target_compile_options(symforce_gen PRIVATE -ffast-math)
+endif()
 target_link_libraries(symforce_gen ${SYMFORCE_EIGEN_TARGET} symforce_lcmtypes_cpp)
 target_include_directories(
   symforce_gen