GNUmakefile: shrink TinyGo binaries on Linux

With these flags, the TinyGo binary gets 17MB (10.6%) smaller. That
seems like a quite useful win for such a small change!

This is only for Linux for now. MacOS and Windows can be tested later,
the flags for those probably need to be modified.

Originally inspired by:
https://discourse.llvm.org/t/state-of-the-art-for-reducing-executable-size-with-heavily-optimized-program/87952/18
There are some other flags like -Wl,--pack-dyn-relocs=relr that did not
shrink binary size in my testing, so I've left them out.

Author: aykevl

.github/workflows/linux.yml

@@ -73,7 +73,7 @@ jobs:
         uses: actions/cache/restore@v4
         id: cache-llvm-build
         with:
-          key: llvm-build-19-linux-alpine-v1
+          key: llvm-build-19-linux-alpine-v2
           path: llvm-build
       - name: Build LLVM
         if: steps.cache-llvm-build.outputs.cache-hit != 'true'
@@ -222,7 +222,7 @@ jobs:
         uses: actions/cache/restore@v4
         id: cache-llvm-build
         with:
-          key: llvm-build-19-linux-asserts-v1
+          key: llvm-build-19-linux-asserts-v2
           path: llvm-build
       - name: Build LLVM
         if: steps.cache-llvm-build.outputs.cache-hit != 'true'
@@ -329,7 +329,7 @@ jobs:
         uses: actions/cache/restore@v4
         id: cache-llvm-build
         with:
-          key: llvm-build-19-linux-${{ matrix.goarch }}-v3
+          key: llvm-build-19-linux-${{ matrix.goarch }}-v4
           path: llvm-build
       - name: Build LLVM
         if: steps.cache-llvm-build.outputs.cache-hit != 'true'

GNUmakefile

@@ -79,6 +79,17 @@ ifeq (1, $(STATIC))
     BINARYEN_OPTION += -DCMAKE_CXX_FLAGS="-static" -DCMAKE_C_FLAGS="-static"
 endif
 
+# Optimize the binary size for Linux.
+# These flags may work on other platforms, but have only been tested on Linux.
+ifeq ($(uname),Linux)
+    LLVM_CFLAGS := -ffunction-sections -fdata-sections -fvisibility=hidden
+    LLVM_LDFLAGS := -Wl,--gc-sections -Wl,--icf=all
+    LLVM_OPTION += \
+        -DCMAKE_C_FLAGS="$(LLVM_CFLAGS)" \
+        -DCMAKE_CXX_FLAGS="$(LLVM_CFLAGS)"
+    CGO_LDFLAGS += $(LLVM_LDFLAGS)
+endif
+
 # Cross compiling support.
 ifneq ($(CROSS),)
     CC = $(CROSS)-gcc