[sycl-post-link] Do not save all split modules in memory (#5021)

Now all split modules are first saved in memory and then processed one by one.
Each split module may require tens of megabytes in memory and total amount of
split modules may be significant. It all may lead to overflow of RAM memory.

Rewrite module splitting in a way that each split module is processed and
immediately saved into a file without temporary collecting all modules in RAM.

Signed-off-by: Mikhail Lychkov <[email protected]>

Author: mlychkov

llvm/test/tools/sycl-post-link/spec-constants/DeprecatedFeautres/spec_const_and_split.ll

@@ -55,5 +55,4 @@ define dso_local spir_kernel void @KERNEL_CCC() {
 ; CHECK-PROP1: SpecConst=2|
 ; CHECK-PROP1-NOT: SpecConst2
 ;
-; CHECK-PROP2: [SYCL/specialization constants]
-; CHECK-PROP2: [SYCL/specialization constants default values]
+; CHECK-PROP2-NOT: [SYCL/specialization constants