[musl] [musl-cross-make] [PATCH] litecross: Fix system header dir when building native toolchains

[Michael Forney]

By default, gcc will search in /usr/include relative to the sysroot,
but musl is configured with an empty prefix, so headers get installed
to /include. This causes gcc to fail to find the libc headers unless
a usr -> . symlink is created manually.

This is not an issue for cross toolchains because in that case, the
configured sysroot is /$(TARGET) which happens to match gcc_tooldir[0],
which is one of gcc's default search directories[1].

The system header directory can be configured with
--with-native-system-header-dir. However, this is not quite sufficient
because the stmp-fixinc target in gcc/Makefile tests for the existence
of that directory relative to the configured sysroot (/)[2]. Most
systems do not have /include, so this fails.

Since musl's fixinc.sh is a no-op[3], we can work around this by
clearing STMP_FIXINC, skipping fixincludes entirely.

[0] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/configure.ac;h=b066cc609e1c2615e66307d5439f765a4f3b286b;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l6319
[1] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/linux.h;h=2ea4ff92c1df9e6d6297996004360ae7eeda2075;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l180
[2] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/Makefile.in;h=20bee0494b1bad4e3ec34e2eae291cf6eadc3aa1;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l3078
[3] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=fixincludes/mkfixinc.sh;h=0f9648608e94f97ab13da223d8192cb04c255772;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l22
---
litecross/Makefile | 2 ++
1 file changed, 2 insertions(+)

diff --git a/litecross/Makefile b/litecross/Makefile
index 2f78157..d1e52b6 100644
--- a/litecross/Makefile
+++ b/litecross/Makefile
@@ -55,6 +55,7 @@ MAKE += MULTILIB_OSDIRNAMES=
MAKE += INFO_DEPS= infodir=
MAKE += ac_cv_prog_lex_root=lex.yy.c
MAKE += MAKEINFO=false
+MAKE += STMP_FIXINC=

FULL_BINUTILS_CONFIG = \
$(COMMON_CONFIG) $(BINUTILS_CONFIG) $(TOOLCHAIN_CONFIG) \
@@ -70,6 +71,7 @@ FULL_GCC_CONFIG = --enable-languages=c,c++ \
--target=$(TARGET) --prefix= \
--libdir=/lib --disable-multilib \
--with-sysroot=$(SYSROOT) \
+ --with-native-system-header-dir=/include \
--enable-tls \
--disable-libmudflap --disable-libsanitizer \
--disable-gnu-indirect-function \