[wasm] Add optimization flags to bitcode compilation (dotnet#101538)

* [wasm] Add optimization flag to bitcode compilation

comping from LD optimization flags.

This should also fix the recent size regression.

* Document the new property

* Update src/mono/browser/build/BrowserWasmApp.targets

Co-authored-by: Larry Ewing <lewing@microsoft.com>

* Fix the conditions

---------

Co-authored-by: Larry Ewing <lewing@microsoft.com>

src/mono/browser/build/BrowserWasmApp.targets

@@ -260,6 +260,8 @@
       <EmccCompileOptimizationFlag Condition="'$(EmccCompileOptimizationFlag)' == ''">$(_EmccOptimizationFlagDefault)</EmccCompileOptimizationFlag>
       <!-- FIXME: which one should take precedence? -->
       <WasmCompileOptimizationFlag>$(EmccCompileOptimizationFlag)</WasmCompileOptimizationFlag>
+      <WasmBitcodeCompileOptimizationFlag Condition="'$(WasmBitcodeCompileOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</WasmBitcodeCompileOptimizationFlag>
+      <WasmBitcodeCompileOptimizationFlag Condition="'$(WasmBitcodeCompileOptimizationFlag)' == '' ">$(WasmCompileOptimizationFlag)</WasmBitcodeCompileOptimizationFlag>
       <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</EmccLinkOptimizationFlag>
       <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == ''"   >$(WasmCompileOptimizationFlag)</EmccLinkOptimizationFlag>
       <WasmLinkOptimizationFlag>$(EmccLinkOptimizationFlag)</WasmLinkOptimizationFlag>
@@ -406,6 +408,7 @@
 
   <Target Name="_BrowserWasmBeforeWriteCompileBitcodeRsp" BeforeTargets="_WasmWriteRspForCompilingBitcode">
     <ItemGroup>
+      <_BitcodeCompileFlags Include="$(WasmBitcodeCompileOptimizationFlag)" />
       <_BitcodeCompileFlags Include="@(_EmccCommonFlags)" />
       <_BitcodeCompileFlags Include="$(EmccExtraBitcodeCompilationFlags)" />
     </ItemGroup>

src/mono/wasi/build/WasiApp.targets

@@ -148,6 +148,8 @@
 
       <WasiClangCompileOptimizationFlag Condition="'$(WasiClangCompileOptimizationFlag)' == ''">$(_WasiClangOptimizationFlagDefault)</WasiClangCompileOptimizationFlag>
       <WasmCompileOptimizationFlag>$(WasiClangCompileOptimizationFlag)</WasmCompileOptimizationFlag>
+      <WasiBitcodeCompileOptimizationFlag Condition="'$(WasiBitcodeCompileOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</WasiBitcodeCompileOptimizationFlag>
+      <WasiBitcodeCompileOptimizationFlag Condition="'$(WasiBitcodeCompileOptimizationFlag)' == ''"   >$(WasiClangCompileOptimizationFlag)</WasiBitcodeCompileOptimizationFlag>
       <WasiClangLinkOptimizationFlag    Condition="'$(WasiClangLinkOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</WasiClangLinkOptimizationFlag>
       <WasiClangLinkOptimizationFlag    Condition="'$(WasiClangLinkOptimizationFlag)' == ''"   >$(WasiClangCompileOptimizationFlag)</WasiClangLinkOptimizationFlag>
       <WasmLinkOptimizationFlag>$(WasiClangLinkOptimizationFlag)</WasmLinkOptimizationFlag>
@@ -265,6 +267,7 @@
   <!-- FIXME: merge with some other target -->
   <Target Name="_WasiBeforeWriteRspForCompilingBitcodeRsp" BeforeTargets="_WasmWriteRspForCompilingBitcode">
     <ItemGroup>
+      <_BitcodeCompileFlags Include="@(WasiBitcodeCompileOptimizationFlag)" />
       <_BitcodeCompileFlags Include="@(_WasiClangCommonFlags)" />
       <_BitcodeCompileFlags Include="$(WasiClangExtraBitcodeCompileFlags)" />
     </ItemGroup>

src/mono/wasm/build/WasmApp.Common.targets

@@ -44,6 +44,8 @@
 
       - $(EmccLinkOptimizationFlag)         - Optimization flag to use for the link step
       - $(EmccCompileOptimizationFlag)      - Optimization flag to use for compiling native files
+      - $(WasmBitcodeCompileOptimizationFlag)
+                                            - Optimization flag to use for compiling bitcode files
 
       - $(EmccFlags)                        - Emcc flags used for both compiling native files, and linking
       - $(EmccExtraLDFlags)                 - Extra emcc flags for linking