Configuring SDL with CMake twice in a row results in different compiler flags

[zopsicle]

Using clang-cl:

$ cmake -G 'Ninja Multi-Config' -B .build
$ cp -R .build backup
$ cmake -G 'Ninja Multi-Config' -B .build
$ diff -ru backup .build

this prints a whole bunch of diff lines like this:

-  FLAGS = /DWIN32 /D_WINDOWS /Ob0 /Od  -MD -Zi /W3 -Wundef -Wfloat-conversion -fno-strict-aliasing -Wdocumentation -Wdocumentation-unknown-command /clang:-fcomment-block-commands=threadsafety -Wshadow -Wno-unused-local-typedefs -Wimplicit-fallthrough -fcolor-diagnostics
+  FLAGS = /DWIN32 /D_WINDOWS /Ob0 /Od /RTC1 -MD -Zi /W3 -Wundef -Wfloat-conversion -fno-strict-aliasing -Wdocumentation -Wdocumentation-unknown-command /clang:-fcomment-block-commands=threadsafety -Wshadow -Wno-unused-local-typedefs -Wimplicit-fallthrough -fcolor-diagnostics

I think the bug is as follows:

SDL/CMakeLists.txt

Line 188 in 62d82ff

if(NOT SDL_LIBC)

this check happens before SDL_LIBC is set. It is not set until here:

SDL/CMakeLists.txt

Line 327 in 62d82ff

set_option(SDL_LIBC "Use the system C library" ${SDL_LIBC_DEFAULT})

The reason it works on the second configure is that SDL_LIBC is read from CMake variable cache.